diff --git a/.github/workflows/sdk-npm-publish.yml b/.github/workflows/sdk-npm-publish.yml
new file mode 100644
index 00000000..6ab45bd1
--- /dev/null
+++ b/.github/workflows/sdk-npm-publish.yml
@@ -0,0 +1,106 @@
+name: Publish SDK to npm
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'packages/sdk/**'
+      - 'package.json'
+      - 'pnpm-lock.yaml'
+      - 'pnpm-workspace.yaml'
+      - 'tsconfig.base.json'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  id-token: write
+
+concurrency:
+  group: sdk-npm-publish-${{ github.ref }}
+  cancel-in-progress: false
+
+jobs:
+  publish:
+    name: Build, test, and publish SDK
+    runs-on: ubuntu-latest
+    environment: SnowLuma
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v6
+        with:
+          version: 10.28.0
+          run_install: false
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v6
+        with:
+          node-version: '22'
+          cache: 'pnpm'
+          registry-url: 'https://registry.npmjs.org'
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Type check SDK
+        run: pnpm --filter @snowluma/sdk typecheck
+
+      - name: Test SDK
+        run: pnpm --filter @snowluma/sdk test
+
+      - name: Build SDK
+        run: pnpm --filter @snowluma/sdk build
+
+      - name: Check npm package version
+        id: npm
+        working-directory: packages/sdk
+        shell: bash
+        run: |
+          set -euo pipefail
+          package_name="$(node -e "const fs = require('node:fs'); console.log(JSON.parse(fs.readFileSync('package.json', 'utf8')).name)")"
+          package_version="$(node -e "const fs = require('node:fs'); console.log(JSON.parse(fs.readFileSync('package.json', 'utf8')).version)")"
+
+          {
+            echo "package_name=${package_name}"
+            echo "package_version=${package_version}"
+          } >> "${GITHUB_OUTPUT}"
+
+          if npm view "${package_name}@${package_version}" version >/dev/null 2>&1; then
+            echo "already_published=true" >> "${GITHUB_OUTPUT}"
+            echo "::notice::${package_name}@${package_version} already exists on npm; skipping publish."
+          else
+            echo "already_published=false" >> "${GITHUB_OUTPUT}"
+          fi
+
+      - name: Validate npm token
+        if: steps.npm.outputs.already_published != 'true'
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}
+        run: |
+          if [ -z "${NODE_AUTH_TOKEN}" ]; then
+            echo 'Missing NPM_TOKEN in the SnowLuma environment secrets.' >&2
+            exit 1
+          fi
+
+      - name: Publish SDK to npm
+        if: steps.npm.outputs.already_published != 'true'
+        working-directory: packages/sdk
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}
+        run: npm publish --access public --provenance
+
+      - name: Summary
+        shell: bash
+        run: |
+          {
+            echo "## SDK npm publish"
+            echo
+            echo "| Key | Value |"
+            echo "| --- | --- |"
+            echo "| Package | \`${{ steps.npm.outputs.package_name }}\` |"
+            echo "| Version | \`${{ steps.npm.outputs.package_version }}\` |"
+            echo "| Already published | \`${{ steps.npm.outputs.already_published }}\` |"
+            echo "| Environment | \`SnowLuma\` |"
+          } >> "${GITHUB_STEP_SUMMARY}"
diff --git a/package.json b/package.json
index 42708386..a1e7ae29 100644
--- a/package.json
+++ b/package.json
@@ -6,8 +6,9 @@
   "type": "module",
   "scripts": {
     "build": "pnpm --filter @snowluma/core build",
+    "build:sdk": "pnpm --filter @snowluma/sdk build",
     "build:webui": "pnpm --filter webui build",
-    "build:all": "pnpm --filter @snowluma/core build:all && pnpm --filter webui build",
+    "build:all": "pnpm --filter @snowluma/core build:all && pnpm --filter @snowluma/sdk build && pnpm --filter webui build",
     "dev": "pnpm --filter @snowluma/core dev",
     "dev:mode": "cd dist && cross-env SNOWLUMA_DEV_MODE=1 SNOWLUMA_DEV_WEBUI=1 node index.mjs",
     "dev:web": "pnpm --filter webui dev",
@@ -32,4 +33,4 @@
   "engines": {
     "node": ">=22"
   }
-}
\ No newline at end of file
+}
diff --git a/packages/sdk/CHANGELOG.md b/packages/sdk/CHANGELOG.md
new file mode 100644
index 00000000..02ea1200
--- /dev/null
+++ b/packages/sdk/CHANGELOG.md
@@ -0,0 +1,8 @@
+# Changelog
+
+## 0.1.0
+
+- Initial SnowLuma TypeScript SDK package.
+- Added HTTP and WebSocket clients for OneBot APIs.
+- Added event middleware, command matching, request context helpers, and message chain builders.
+- Added structured SDK error classes and per-request `AbortSignal` support.
diff --git a/packages/sdk/README.md b/packages/sdk/README.md
new file mode 100644
index 00000000..cc36a41a
--- /dev/null
+++ b/packages/sdk/README.md
@@ -0,0 +1,259 @@
+# @snowluma/sdk
+
+SnowLuma 的 TypeScript SDK，提供 OneBot HTTP / WebSocket 客户端、事件中间件、命令匹配和消息链式构造器。
+
+## 导航
+
+- [安装](#安装)
+- [快速开始](#快速开始)
+- [HTTP Client](#http-client)
+- [WebSocket Client](#websocket-client)
+- [事件中间件与命令](#事件中间件与命令)
+- [Raw Action](#raw-action)
+- [Message Builder](#message-builder)
+- [请求控制](#请求控制)
+- [错误处理](#错误处理)
+- [测试建议](#测试建议)
+- [子路径导入](#子路径导入)
+- [Action 同步](#action-同步)
+- [项目结构](#项目结构)
+- [版本策略](#版本策略)
+
+## 安装
+
+在本 monorepo 内直接通过 workspace 引用：
+
+```bash
+pnpm add @snowluma/sdk --workspace
+```
+
+发布到 npm 后可直接安装：
+
+```bash
+pnpm add @snowluma/sdk
+```
+
+## 快速开始
+
+```ts
+import { SnowLumaHttpClient, text } from '@snowluma/sdk';
+
+const bot = new SnowLumaHttpClient({
+  baseUrl: 'http://127.0.0.1:3000/',
+  accessToken: process.env.SNOWLUMA_TOKEN,
+});
+
+const login = await bot.getLoginInfo();
+await bot.sendGroupMessage(123456, text(`Hello from ${login.nickname}`).at('all'));
+```
+
+SnowLuma 的 OneBot HTTP / WebSocket 端口和 `accessToken` 来自 `config/onebot_<uin>.json`。
+
+## HTTP Client
+
+```ts
+import { SnowLumaHttpClient, message, text } from '@snowluma/sdk';
+
+const bot = new SnowLumaHttpClient({
+  baseUrl: 'http://127.0.0.1:3000/',
+  accessToken: process.env.SNOWLUMA_TOKEN,
+  requestTimeoutMs: 30_000,
+});
+
+await bot.sendPrivateMessage(10001, text('pong'));
+
+await bot.sendGroupMessage(123456, [
+  message.text('Hello'),
+  message.at('all'),
+]);
+```
+
+## WebSocket Client
+
+WebSocket 客户端会用 `echo` 关联 API 响应，并把无 `echo` 的包作为事件分发。
+
+```ts
+import { SnowLumaWebSocketClient, text } from '@snowluma/sdk';
+
+const bot = new SnowLumaWebSocketClient({
+  url: 'ws://127.0.0.1:3001/',
+  accessToken: process.env.SNOWLUMA_TOKEN,
+  reconnect: true,
+});
+
+bot.onGroupMessage(async (event, ctx) => {
+  if (event.raw_message === '/ping') {
+    await ctx.reply(text('pong').at(event.user_id));
+  }
+});
+
+bot.onRequest('friend', async (_event, ctx) => {
+  await ctx.approve();
+});
+
+await bot.connect();
+await bot.sendPrivateMessage(10001, text('ready'));
+```
+
+## 事件中间件与命令
+
+```ts
+bot.use(async (event, ctx, next) => {
+  console.log(event.post_type);
+  await next();
+});
+
+bot.command('echo', async (_event, ctx, match) => {
+  await ctx.reply(text(match.rest || 'empty'));
+});
+
+bot.when(
+  (event) => event.post_type === 'notice',
+  async (event) => console.log(event),
+);
+```
+
+事件上下文内置快捷操作：
+
+- `ctx.reply(message)`：按私聊/群聊自动回复。
+- `ctx.approve()` / `ctx.reject(reason)`：处理好友或群请求。
+- `ctx.quickOperation(operation)`：调用 `.handle_quick_operation`。
+- `ctx.stopPropagation()`：停止后续中间件和普通 `onEvent` 分发。
+
+## Raw Action
+
+高频接口提供 camelCase 方法；其它 SnowLuma action 可以用 `raw` 或 `rawResponse`：
+
+```ts
+const data = await bot.raw('get_group_file_system_info', {
+  group_id: 123456,
+});
+
+const response = await bot.rawResponse('get_status');
+```
+
+`raw` 会在 SnowLuma 返回 `status: "failed"` 或非零 `retcode` 时抛出 `SnowLumaApiError`；`rawResponse` 会保留完整响应。
+
+## Message Builder
+
+```ts
+import { fromCQString, message, text, toCQString } from '@snowluma/sdk';
+
+const segments = [
+  message.reply(42),
+  message.text('收到 '),
+  message.image('https://example.com/a.png'),
+];
+
+const chained = text('收到 ')
+  .at(10001)
+  .image('https://example.com/a.png');
+
+const cq = toCQString(segments);
+const chainedCq = toCQString(chained);
+const parsed = fromCQString('hi[CQ:at,qq=all]');
+```
+
+链式入口返回 `MessageChain`，可以直接传给发送接口，也可以用 `build()` / `toSegments()` 转成 OneBot segment 数组：
+
+```ts
+await bot.sendGroupMessage(123456, text('hi').at(10001).image('/tmp/a.png'));
+
+const segments = text('hi').at('all').build();
+
+await text('hi').atAll().br().face(14).sendToGroup(bot, 123456);
+```
+
+`reply()` 在一条链中只能出现一次；TypeScript 会阻止 `text('a').reply(1).reply(2)`，运行时也会做同样检查。
+
+已内置常用段：`text`、`br`、`face`、`at`、`atAll`、`reply`、`image`、`record`、`video`、`json`、`xml`、`poke`、`forward`、`node`、`share`、`music`、`location`、`contact` 和 `raw`。
+
+## 请求控制
+
+每次请求都支持覆盖 `echo`、超时和 `AbortSignal`：
+
+```ts
+const controller = new AbortController();
+
+const status = bot.getStatus({
+  echo: 'healthcheck',
+  timeoutMs: 5_000,
+  signal: controller.signal,
+});
+
+controller.abort();
+await status;
+```
+
+`timeoutMs: 0` 表示关闭该请求的超时控制。
+
+## 错误处理
+
+SDK 暴露统一错误基类和更具体的错误类型：
+
+- `SnowLumaApiError`：OneBot 响应失败或 `retcode !== 0`。
+- `SnowLumaAuthError`：鉴权相关 retcode，例如 `1401`、`401`、`403`。
+- `SnowLumaTransportError`：连接、解析、超时、取消等传输层错误基类。
+- `SnowLumaConnectionError`：HTTP fetch / WebSocket 连接或发送失败。
+- `SnowLumaParseError`：响应不是合法 JSON 或不符合 OneBot 响应结构。
+- `SnowLumaTimeoutError`：请求超过 `timeoutMs`。
+- `SnowLumaAbortError`：调用方通过 `AbortSignal` 主动取消。
+
+```ts
+import {
+  SnowLumaApiError,
+  SnowLumaAuthError,
+  SnowLumaTimeoutError,
+} from '@snowluma/sdk';
+
+try {
+  await bot.getStatus({ timeoutMs: 1000 });
+} catch (error) {
+  if (error instanceof SnowLumaAuthError) {
+    throw new Error('SnowLuma access token is invalid');
+  }
+  if (error instanceof SnowLumaTimeoutError) {
+    console.warn(`SnowLuma did not respond in ${error.timeoutMs}ms`);
+  }
+  if (error instanceof SnowLumaApiError) {
+    console.warn(error.retcode, error.wording);
+  }
+}
+```
+
+## 测试建议
+
+- SDK 自身使用 Vitest 覆盖消息构造、事件上下文、WebSocket 响应关联、错误模型和取消逻辑。
+- 对接真实 SnowLuma 时建议使用单独测试账号和测试群，避免把自动化消息发到生产环境。
+- 集成测试里优先显式设置 `echo` 和较短 `timeoutMs`，这样失败时更容易定位是哪一次 action。
+- 发布前运行 `pnpm --filter @snowluma/sdk typecheck`、`pnpm --filter @snowluma/sdk test`、`pnpm --filter @snowluma/sdk build`。
+
+## 子路径导入
+
+```ts
+import { SnowLumaHttpClient } from '@snowluma/sdk/client';
+import { text } from '@snowluma/sdk/messages';
+import { isMessageEvent } from '@snowluma/sdk/events';
+import { SnowLumaApiError } from '@snowluma/sdk/errors';
+```
+
+根入口 `@snowluma/sdk` 仍导出正式公开 API；不再保留旧的根级兼容 barrel 或别名 API。
+
+## Action 同步
+
+SDK 导出 `SNOWLUMA_ACTIONS` 和 `isSnowLumaAction()`。测试会扫描 `packages/core/src/onebot/actions/*.ts` 的 `registerAction()`，确保 SDK action 列表没有落后。
+
+## 项目结构
+
+```text
+src/
+  client/      HTTP / WebSocket client 与 API facade
+  events/      事件上下文、类型守卫、中间件和命令匹配
+  messages/    segment 工厂、MessageChain、CQ 编解码
+  types/       JSON、消息、事件、action 参数和返回类型
+  internal/    SDK 内部工具
+```
+
+## 版本策略
+
+当前包版本为 `0.1.0`。版本规则、发布检查清单和破坏性变更边界见 [VERSIONING.md](./VERSIONING.md)。
diff --git a/packages/sdk/VERSIONING.md b/packages/sdk/VERSIONING.md
new file mode 100644
index 00000000..1465a227
--- /dev/null
+++ b/packages/sdk/VERSIONING.md
@@ -0,0 +1,43 @@
+# @snowluma/sdk Versioning
+
+The SDK follows SemVer for its public package surface:
+
+- Exported runtime values and classes from `@snowluma/sdk`.
+- Exported types from `@snowluma/sdk` and `@snowluma/sdk/types`.
+- Supported subpath exports: `client`, `messages`, `events`, `errors`, `actions`, and `types`.
+- Runtime behavior of typed client helpers, message builders, event helpers, and SDK error classes.
+
+## Current 0.x Policy
+
+While the SDK is below `1.0.0`, breaking changes should use a minor release and include a migration note. Patch releases should remain bug fixes only.
+
+Examples:
+
+- `0.1.1`: bug fix, doc fix, type refinement that does not break consumers.
+- `0.2.0`: new client helper, new event helper, new action typing, or documented breaking change before 1.0.
+- `1.0.0`: first stable release where breaking changes move to major versions.
+
+## After 1.0
+
+- Major: removes or changes a public export, changes runtime behavior incompatibly, changes supported Node version, or changes package subpaths.
+- Minor: adds new public API, supports new SnowLuma actions, adds optional parameters, or adds error subclasses.
+- Patch: fixes bugs, improves docs, narrows implementation details without breaking public types, or updates action metadata without changing call signatures.
+
+## Release Checklist
+
+1. Update `packages/sdk/package.json` version.
+2. Update `packages/sdk/CHANGELOG.md`.
+3. Run `pnpm --filter @snowluma/sdk typecheck`.
+4. Run `pnpm --filter @snowluma/sdk test`.
+5. Run `pnpm --filter @snowluma/sdk build`.
+6. Run `pnpm --filter @snowluma/sdk pack --dry-run` to inspect published files.
+
+## Automated npm Publish
+
+`.github/workflows/sdk-npm-publish.yml` publishes `@snowluma/sdk` when SDK-related files reach `main`, including the automated `dev` to `main` promotion flow. The publish job uses the GitHub Environment named `SnowLuma` and expects an environment secret named `NPM_TOKEN`.
+
+If the package version already exists on npm, the workflow skips publishing that run. Bump `packages/sdk/package.json` before merging SDK changes that should create a new npm release.
+
+## Action Compatibility
+
+SnowLuma action coverage is synchronized from `packages/core/src/onebot/actions/*.ts`. Adding an action type is a minor change unless it changes an existing method signature or return type.
diff --git a/packages/sdk/package.json b/packages/sdk/package.json
new file mode 100644
index 00000000..031e0be0
--- /dev/null
+++ b/packages/sdk/package.json
@@ -0,0 +1,95 @@
+{
+  "name": "@snowluma/sdk",
+  "author": {
+    "name": "MotricSeven",
+    "email": "motricseven@gmail.com"
+  },
+  "version": "0.1.0",
+  "description": "TypeScript SDK for SnowLuma OneBot HTTP and WebSocket transports",
+  "keywords": [
+    "snowluma",
+    "onebot",
+    "onebot11",
+    "qq",
+    "bot",
+    "sdk"
+  ],
+  "homepage": "https://github.com/SnowLuma/SnowLuma#readme",
+  "bugs": {
+    "url": "https://github.com/SnowLuma/SnowLuma/issues"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/SnowLuma/SnowLuma.git",
+    "directory": "packages/sdk"
+  },
+  "license": "UNLICENSED",
+  "type": "module",
+  "sideEffects": false,
+  "main": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js"
+    },
+    "./client": {
+      "types": "./dist/client/index.d.ts",
+      "import": "./dist/client/index.js"
+    },
+    "./messages": {
+      "types": "./dist/messages/index.d.ts",
+      "import": "./dist/messages/index.js"
+    },
+    "./events": {
+      "types": "./dist/events/index.d.ts",
+      "import": "./dist/events/index.js"
+    },
+    "./types": {
+      "types": "./dist/types/index.d.ts",
+      "import": "./dist/types/index.js"
+    },
+    "./errors": {
+      "types": "./dist/errors.d.ts",
+      "import": "./dist/errors.js"
+    },
+    "./actions": {
+      "types": "./dist/actions.d.ts",
+      "import": "./dist/actions.js"
+    },
+    "./package.json": "./package.json"
+  },
+  "files": [
+    "dist/actions.*",
+    "dist/client",
+    "dist/emitter.*",
+    "dist/errors.*",
+    "dist/events",
+    "dist/index.*",
+    "dist/internal",
+    "dist/messages",
+    "dist/types",
+    "README.md",
+    "CHANGELOG.md",
+    "VERSIONING.md"
+  ],
+  "scripts": {
+    "clean": "node -e \"const fs = require('node:fs'); fs.rmSync('dist', { recursive: true, force: true })\"",
+    "prebuild": "pnpm run clean",
+    "build": "tsc -p tsconfig.json",
+    "prepack": "pnpm run build",
+    "test": "vitest run",
+    "typecheck": "tsc --noEmit"
+  },
+  "publishConfig": {
+    "access": "public"
+  },
+  "engines": {
+    "node": ">=22"
+  },
+  "devDependencies": {
+    "@types/node": "^24.12.2",
+    "typescript": "catalog:",
+    "vitest": "^4.1.4"
+  }
+}
diff --git a/packages/sdk/src/actions.ts b/packages/sdk/src/actions.ts
new file mode 100644
index 00000000..c8e6b44e
--- /dev/null
+++ b/packages/sdk/src/actions.ts
@@ -0,0 +1,126 @@
+import type { SnowLumaActionMap } from './types/index';
+
+export const SNOWLUMA_ACTIONS = [
+  'get_login_info',
+  'get_status',
+  'get_version_info',
+  'can_send_image',
+  'can_send_record',
+  'send_msg',
+  'send_private_msg',
+  'send_group_msg',
+  'get_msg',
+  'delete_msg',
+  'get_friend_list',
+  'get_stranger_info',
+  'delete_friend',
+  'get_group_list',
+  'get_group_info',
+  'get_group_member_list',
+  'get_group_member_info',
+  'get_group_honor_info',
+  'get_group_system_msg',
+  'set_group_kick',
+  'set_group_ban',
+  'set_group_whole_ban',
+  'set_group_admin',
+  'set_group_card',
+  'set_group_name',
+  'set_group_leave',
+  'set_group_special_title',
+  'set_group_anonymous',
+  'set_group_anonymous_ban',
+  'set_group_portrait',
+  'upload_group_file',
+  'upload_private_file',
+  'get_group_file_url',
+  'get_group_root_files',
+  'get_group_files_by_folder',
+  'delete_group_file',
+  'move_group_file',
+  'create_group_file_folder',
+  'delete_group_file_folder',
+  'rename_group_file_folder',
+  'get_private_file_url',
+  'set_friend_add_request',
+  'set_group_add_request',
+  'send_like',
+  'friend_poke',
+  'group_poke',
+  'send_poke',
+  'set_essence_msg',
+  'delete_essence_msg',
+  'get_essence_msg_list',
+  'set_group_reaction',
+  'get_group_msg_history',
+  'get_friend_msg_history',
+  'mark_group_msg_as_read',
+  'mark_private_msg_as_read',
+  'mark_msg_as_read',
+  'get_rkey',
+  'ocr_image',
+  '.ocr_image',
+  '_send_group_notice',
+  '_get_group_notice',
+  '_del_group_notice',
+  'upload_forward_msg',
+  'upload_foward_msg',
+  'send_forward_msg',
+  'send_group_forward_msg',
+  'send_private_forward_msg',
+  'get_forward_msg',
+  'get_image',
+  'get_record',
+  'get_cookies',
+  'get_csrf_token',
+  'get_credentials',
+  'set_restart',
+  'clean_cache',
+  '.handle_quick_operation',
+  'set_friend_remark',
+  'set_msg_emoji_like',
+  '_mark_all_as_read',
+  'get_group_file_system_info',
+  'check_url_safely',
+  'download_file',
+  'set_qq_profile',
+  'set_online_status',
+  'get_group_ignored_notifies',
+  'get_group_shut_list',
+  'forward_friend_single_msg',
+  'forward_group_single_msg',
+  'get_recent_contact',
+  'get_profile_like',
+  'get_friends_with_category',
+  'get_online_clients',
+  '_get_model_show',
+  '_set_model_show',
+  '.get_word_slices',
+  'get_group_at_all_remain',
+  'get_unidirectional_friend_list',
+  'set_self_longnick',
+  'get_collection_list',
+  'create_collection',
+  'set_qq_avatar',
+  'set_input_status',
+  'translate_en2zh',
+  'get_clientkey',
+  'get_mini_app_ark',
+  'click_inline_keyboard_button',
+  'set_group_sign',
+  'send_group_sign',
+  'get_group_info_ex',
+  'get_group_detail_info',
+  'trans_group_file',
+  'rename_group_file',
+  'get_file',
+  '.send_packet',
+] as const satisfies readonly (keyof SnowLumaActionMap)[];
+
+export type SnowLumaKnownAction = typeof SNOWLUMA_ACTIONS[number];
+
+const ACTION_SET = new Set<string>(SNOWLUMA_ACTIONS);
+
+export function isSnowLumaAction(action: string): action is SnowLumaKnownAction {
+  return ACTION_SET.has(action);
+}
diff --git a/packages/sdk/src/client/api-client.ts b/packages/sdk/src/client/api-client.ts
new file mode 100644
index 00000000..a05d5128
--- /dev/null
+++ b/packages/sdk/src/client/api-client.ts
@@ -0,0 +1,470 @@
+import { createSnowLumaApiError } from '../errors';
+import { normalizeMessage } from '../messages/index';
+import type {
+  ActionParams,
+  ActionResult,
+  ApiResponse,
+  DomainParams,
+  DownloadFileParams,
+  ForwardMessageParams,
+  GetForwardMsgParams,
+  GetFriendMessageHistoryParams,
+  GetGroupHonorInfoParams,
+  GetGroupMessageHistoryParams,
+  GetMediaParams,
+  JsonObject,
+  JsonValue,
+  OutgoingMessage,
+  PrivateForwardMessageParams,
+  RequestOptions,
+  SendMsgParams,
+  SetGroupReactionParams,
+  SnowLumaAction,
+} from '../types/index';
+
+/**
+ * Base class for SnowLuma API clients.
+ *
+ * Concrete transports implement request(); this facade adds typed OneBot actions,
+ * message normalization, and failed-response error handling.
+ */
+export abstract class SnowLumaApiClient {
+  /** Sends a raw OneBot action and returns the complete API response. */
+  abstract request<TAction extends SnowLumaAction>(
+    action: TAction,
+    params?: ActionParams<TAction>,
+    options?: RequestOptions,
+  ): Promise<ApiResponse<ActionResult<TAction>>>;
+
+  /** Sends a OneBot action and returns data, throwing SnowLumaApiError on failed responses. */
+  async call<TAction extends SnowLumaAction>(
+    action: TAction,
+    params?: ActionParams<TAction>,
+    options?: RequestOptions,
+  ): Promise<ActionResult<TAction>> {
+    const response = await this.request(action, params, options);
+    if (response.status !== 'ok' || response.retcode !== 0) {
+      throw createSnowLumaApiError(response);
+    }
+    return response.data;
+  }
+
+  getLoginInfo(options?: RequestOptions) {
+    return this.call('get_login_info', {}, options);
+  }
+
+  getStatus(options?: RequestOptions) {
+    return this.call('get_status', {}, options);
+  }
+
+  getVersionInfo(options?: RequestOptions) {
+    return this.call('get_version_info', {}, options);
+  }
+
+  canSendImage(options?: RequestOptions) {
+    return this.call('can_send_image', {}, options);
+  }
+
+  canSendRecord(options?: RequestOptions) {
+    return this.call('can_send_record', {}, options);
+  }
+
+  sendMsg(params: Omit<SendMsgParams, 'message'> & { message: OutgoingMessage }, options?: RequestOptions) {
+    return this.call('send_msg', { ...params, message: normalizeMessage(params.message) as JsonValue }, options);
+  }
+
+  sendPrivateMessage(userId: number, message: OutgoingMessage, options?: RequestOptions & { autoEscape?: boolean }) {
+    return this.call('send_private_msg', {
+      user_id: userId,
+      message: normalizeMessage(message) as JsonValue,
+      auto_escape: options?.autoEscape,
+    }, options);
+  }
+
+  sendGroupMessage(groupId: number, message: OutgoingMessage, options?: RequestOptions & { autoEscape?: boolean }) {
+    return this.call('send_group_msg', {
+      group_id: groupId,
+      message: normalizeMessage(message) as JsonValue,
+      auto_escape: options?.autoEscape,
+    }, options);
+  }
+
+  getMessage(messageId: number, options?: RequestOptions) {
+    return this.call('get_msg', { message_id: messageId }, options);
+  }
+
+  deleteMessage(messageId: number, options?: RequestOptions) {
+    return this.call('delete_msg', { message_id: messageId }, options);
+  }
+
+  getFriendList(options?: RequestOptions) {
+    return this.call('get_friend_list', {}, options);
+  }
+
+  getStrangerInfo(userId: number, options?: RequestOptions) {
+    return this.call('get_stranger_info', { user_id: userId }, options);
+  }
+
+  deleteFriend(userId: number, options?: RequestOptions & { block?: boolean }) {
+    return this.call('delete_friend', { user_id: userId, block: options?.block }, options);
+  }
+
+  getGroupList(options?: RequestOptions & { noCache?: boolean }) {
+    return this.call('get_group_list', { no_cache: options?.noCache }, options);
+  }
+
+  getGroupInfo(groupId: number, options?: RequestOptions & { noCache?: boolean }) {
+    return this.call('get_group_info', { group_id: groupId, no_cache: options?.noCache }, options);
+  }
+
+  getGroupMemberList(groupId: number, options?: RequestOptions & { noCache?: boolean }) {
+    return this.call('get_group_member_list', { group_id: groupId, no_cache: options?.noCache }, options);
+  }
+
+  getGroupMemberInfo(groupId: number, userId: number, options?: RequestOptions & { noCache?: boolean }) {
+    return this.call('get_group_member_info', {
+      group_id: groupId,
+      user_id: userId,
+      no_cache: options?.noCache,
+    }, options);
+  }
+
+  getGroupHonorInfo(params: GetGroupHonorInfoParams, options?: RequestOptions) {
+    return this.call('get_group_honor_info', params, options);
+  }
+
+  getGroupSystemMessages(options?: RequestOptions) {
+    return this.call('get_group_system_msg', {}, options);
+  }
+
+  setGroupKick(groupId: number, userId: number, options?: RequestOptions & { rejectAddRequest?: boolean }) {
+    return this.call('set_group_kick', {
+      group_id: groupId,
+      user_id: userId,
+      reject_add_request: options?.rejectAddRequest,
+    }, options);
+  }
+
+  setGroupBan(groupId: number, userId: number, duration?: number, options?: RequestOptions) {
+    return this.call('set_group_ban', { group_id: groupId, user_id: userId, duration }, options);
+  }
+
+  setGroupWholeBan(groupId: number, enable = true, options?: RequestOptions) {
+    return this.call('set_group_whole_ban', { group_id: groupId, enable }, options);
+  }
+
+  setGroupAdmin(groupId: number, userId: number, enable = true, options?: RequestOptions) {
+    return this.call('set_group_admin', { group_id: groupId, user_id: userId, enable }, options);
+  }
+
+  setGroupCard(groupId: number, userId: number, card = '', options?: RequestOptions) {
+    return this.call('set_group_card', { group_id: groupId, user_id: userId, card }, options);
+  }
+
+  setGroupName(groupId: number, name: string, options?: RequestOptions) {
+    return this.call('set_group_name', { group_id: groupId, group_name: name }, options);
+  }
+
+  setGroupLeave(groupId: number, options?: RequestOptions) {
+    return this.call('set_group_leave', { group_id: groupId }, options);
+  }
+
+  setGroupSpecialTitle(groupId: number, userId: number, title = '', options?: RequestOptions) {
+    return this.call('set_group_special_title', {
+      group_id: groupId,
+      user_id: userId,
+      special_title: title,
+    }, options);
+  }
+
+  uploadGroupFile(groupId: number, file: string, options: RequestOptions & {
+    name?: string;
+    folder?: string;
+    folderId?: string;
+    uploadFile?: boolean;
+  } = {}) {
+    return this.call('upload_group_file', {
+      group_id: groupId,
+      file,
+      name: options.name,
+      folder: options.folder,
+      folder_id: options.folderId,
+      upload_file: options.uploadFile,
+    }, options);
+  }
+
+  uploadPrivateFile(userId: number, file: string, options: RequestOptions & {
+    name?: string;
+    uploadFile?: boolean;
+  } = {}) {
+    return this.call('upload_private_file', {
+      user_id: userId,
+      file,
+      name: options.name,
+      upload_file: options.uploadFile,
+    }, options);
+  }
+
+  getGroupFileUrl(groupId: number, fileId: string, options?: RequestOptions & { busid?: number }) {
+    return this.call('get_group_file_url', { group_id: groupId, file_id: fileId, busid: options?.busid }, options);
+  }
+
+  getGroupRootFiles(groupId: number, options?: RequestOptions) {
+    return this.call('get_group_root_files', { group_id: groupId }, options);
+  }
+
+  getGroupFilesByFolder(groupId: number, folderId = '/', options?: RequestOptions) {
+    return this.call('get_group_files_by_folder', { group_id: groupId, folder_id: folderId }, options);
+  }
+
+  deleteGroupFile(groupId: number, fileId: string, options?: RequestOptions) {
+    return this.call('delete_group_file', { group_id: groupId, file_id: fileId }, options);
+  }
+
+  moveGroupFile(groupId: number, fileId: string, parentDirectory: string, targetDirectory: string, options?: RequestOptions) {
+    return this.call('move_group_file', {
+      group_id: groupId,
+      file_id: fileId,
+      parent_directory: parentDirectory,
+      target_directory: targetDirectory,
+    }, options);
+  }
+
+  createGroupFileFolder(groupId: number, name: string, parentId = '/', options?: RequestOptions) {
+    return this.call('create_group_file_folder', { group_id: groupId, name, parent_id: parentId }, options);
+  }
+
+  deleteGroupFileFolder(groupId: number, folderId: string, options?: RequestOptions) {
+    return this.call('delete_group_file_folder', { group_id: groupId, folder_id: folderId }, options);
+  }
+
+  renameGroupFileFolder(groupId: number, folderId: string, newName: string, options?: RequestOptions) {
+    return this.call('rename_group_file_folder', {
+      group_id: groupId,
+      folder_id: folderId,
+      new_folder_name: newName,
+    }, options);
+  }
+
+  getPrivateFileUrl(userId: number, fileId: string, fileHash: string, options?: RequestOptions) {
+    return this.call('get_private_file_url', { user_id: userId, file_id: fileId, file_hash: fileHash }, options);
+  }
+
+  setFriendAddRequest(flag: string, approve = true, options?: RequestOptions) {
+    return this.call('set_friend_add_request', { flag, approve }, options);
+  }
+
+  setGroupAddRequest(flag: string, params: RequestOptions & {
+    subType?: string;
+    type?: string;
+    approve?: boolean;
+    reason?: string;
+  } = {}) {
+    return this.call('set_group_add_request', {
+      flag,
+      sub_type: params.subType,
+      type: params.type,
+      approve: params.approve,
+      reason: params.reason,
+    }, params);
+  }
+
+  sendLike(userId: number, times = 1, options?: RequestOptions) {
+    return this.call('send_like', { user_id: userId, times }, options);
+  }
+
+  friendPoke(userId: number, options?: RequestOptions & { targetId?: number }) {
+    return this.call('friend_poke', { user_id: userId, target_id: options?.targetId }, options);
+  }
+
+  groupPoke(groupId: number, userId: number, options?: RequestOptions) {
+    return this.call('group_poke', { group_id: groupId, user_id: userId }, options);
+  }
+
+  sendPoke(userId: number, options?: RequestOptions & { groupId?: number }) {
+    return this.call('send_poke', { user_id: userId, group_id: options?.groupId }, options);
+  }
+
+  setEssenceMessage(messageId: number, options?: RequestOptions) {
+    return this.call('set_essence_msg', { message_id: messageId }, options);
+  }
+
+  deleteEssenceMessage(messageId: number, options?: RequestOptions) {
+    return this.call('delete_essence_msg', { message_id: messageId }, options);
+  }
+
+  getEssenceMessageList(groupId: number, options?: RequestOptions) {
+    return this.call('get_essence_msg_list', { group_id: groupId }, options);
+  }
+
+  setGroupReaction(params: SetGroupReactionParams, options?: RequestOptions) {
+    return this.call('set_group_reaction', params, options);
+  }
+
+  getGroupMessageHistory(params: GetGroupMessageHistoryParams, options?: RequestOptions) {
+    return this.call('get_group_msg_history', params, options);
+  }
+
+  getFriendMessageHistory(params: GetFriendMessageHistoryParams, options?: RequestOptions) {
+    return this.call('get_friend_msg_history', params, options);
+  }
+
+  markGroupMessageAsRead(messageId: number, groupId?: number, options?: RequestOptions) {
+    return this.call('mark_group_msg_as_read', { message_id: messageId, group_id: groupId }, options);
+  }
+
+  markPrivateMessageAsRead(messageId: number, userId?: number, options?: RequestOptions) {
+    return this.call('mark_private_msg_as_read', { message_id: messageId, user_id: userId }, options);
+  }
+
+  markMessageAsRead(messageId: number, targetId?: number, options?: RequestOptions) {
+    return this.call('mark_msg_as_read', { message_id: messageId, target_id: targetId }, options);
+  }
+
+  getRKey(options?: RequestOptions) {
+    return this.call('get_rkey', {}, options);
+  }
+
+  sendGroupNotice(groupId: number, content: string, options: RequestOptions & {
+    image?: string;
+    pinned?: number;
+    type?: number;
+    confirmRequired?: number;
+  } = {}) {
+    return this.call('_send_group_notice', {
+      group_id: groupId,
+      content,
+      image: options.image,
+      pinned: options.pinned,
+      type: options.type,
+      confirm_required: options.confirmRequired,
+    }, options);
+  }
+
+  getGroupNotice(groupId: number, options?: RequestOptions) {
+    return this.call('_get_group_notice', { group_id: groupId }, options);
+  }
+
+  uploadForwardMessage(params: ForwardMessageParams, options?: RequestOptions) {
+    return this.call('upload_forward_msg', params, options);
+  }
+
+  sendForwardMessage(params: ForwardMessageParams, options?: RequestOptions) {
+    return this.call('send_forward_msg', params, options);
+  }
+
+  sendGroupForwardMessage(groupId: number, messages: OutgoingMessage, options?: RequestOptions) {
+    return this.call('send_group_forward_msg', {
+      group_id: groupId,
+      messages: normalizeMessage(messages) as JsonValue,
+    }, options);
+  }
+
+  sendPrivateForwardMessage(userId: number, messages: OutgoingMessage, options?: RequestOptions) {
+    return this.call('send_private_forward_msg', {
+      user_id: userId,
+      messages: normalizeMessage(messages) as JsonValue,
+    }, options);
+  }
+
+  getForwardMessage(params: GetForwardMsgParams, options?: RequestOptions) {
+    return this.call('get_forward_msg', params, options);
+  }
+
+  getImage(params: GetMediaParams, options?: RequestOptions) {
+    return this.call('get_image', params, options);
+  }
+
+  getRecord(params: GetMediaParams, options?: RequestOptions) {
+    return this.call('get_record', params, options);
+  }
+
+  getCookies(params: DomainParams = {}, options?: RequestOptions) {
+    return this.call('get_cookies', params, options);
+  }
+
+  getCsrfToken(options?: RequestOptions) {
+    return this.call('get_csrf_token', {}, options);
+  }
+
+  getCredentials(params: DomainParams = {}, options?: RequestOptions) {
+    return this.call('get_credentials', params, options);
+  }
+
+  cleanCache(options?: RequestOptions) {
+    return this.call('clean_cache', {}, options);
+  }
+
+  setFriendRemark(userId: number, remark: string, options?: RequestOptions) {
+    return this.call('set_friend_remark', { user_id: userId, remark }, options);
+  }
+
+  setMsgEmojiLike(messageId: number, emojiId: string, set = true, options?: RequestOptions) {
+    return this.call('set_msg_emoji_like', { message_id: messageId, emoji_id: emojiId, set }, options);
+  }
+
+  markAllAsRead(options?: RequestOptions) {
+    return this.call('_mark_all_as_read', {}, options);
+  }
+
+  getGroupFileSystemInfo(groupId: number, options?: RequestOptions) {
+    return this.call('get_group_file_system_info', { group_id: groupId }, options);
+  }
+
+  checkUrlSafely(options?: RequestOptions) {
+    return this.call('check_url_safely', {}, options);
+  }
+
+  downloadFile(params: DownloadFileParams, options?: RequestOptions) {
+    return this.call('download_file', params, options);
+  }
+
+  setQqProfile(params: { nickname?: string; personalNote?: string }, options?: RequestOptions) {
+    return this.call('set_qq_profile', {
+      nickname: params.nickname,
+      personal_note: params.personalNote,
+    }, options);
+  }
+
+  setOnlineStatus(status: number, params: RequestOptions & { extStatus?: number; batteryStatus?: number } = {}) {
+    return this.call('set_online_status', {
+      status,
+      ext_status: params.extStatus,
+      battery_status: params.batteryStatus,
+    }, params);
+  }
+
+  getClientKey(options?: RequestOptions) {
+    return this.call('get_clientkey', {}, options);
+  }
+
+  getGroupInfoEx(groupId: number, options?: RequestOptions) {
+    return this.call('get_group_info_ex', { group_id: groupId }, options);
+  }
+
+  getGroupDetailInfo(groupId: number, options?: RequestOptions) {
+    return this.call('get_group_detail_info', { group_id: groupId }, options);
+  }
+
+  /** Calls any registered SnowLuma action and returns the response data. */
+  raw<TAction extends SnowLumaAction>(
+    action: TAction,
+    params?: ActionParams<TAction>,
+    options?: RequestOptions,
+  ) {
+    return this.call(action, params, options);
+  }
+
+  /** Calls any registered SnowLuma action and preserves the full OneBot response envelope. */
+  rawResponse<TAction extends SnowLumaAction>(
+    action: TAction,
+    params?: ActionParams<TAction>,
+    options?: RequestOptions,
+  ) {
+    return this.request(action, params, options);
+  }
+}
+
+export function toJsonObject(value: JsonObject | undefined): JsonObject {
+  return value ?? {};
+}
diff --git a/packages/sdk/src/client/http-client.ts b/packages/sdk/src/client/http-client.ts
new file mode 100644
index 00000000..95495ca1
--- /dev/null
+++ b/packages/sdk/src/client/http-client.ts
@@ -0,0 +1,115 @@
+import {
+  SnowLumaAbortError,
+  SnowLumaConnectionError,
+  SnowLumaParseError,
+  SnowLumaTimeoutError,
+  SnowLumaTransportError,
+} from '../errors';
+import { SnowLumaApiClient, toJsonObject } from './api-client';
+import { createRequestAbortState, isAbortError } from '../internal/abort';
+import { assertApiResponse } from '../internal/json';
+import type {
+  ActionParams,
+  ActionResult,
+  ApiResponse,
+  JsonObject,
+  RequestOptions,
+  SnowLumaAction,
+  SnowLumaClientOptions,
+} from '../types/index';
+
+/** Options for the HTTP transport client. */
+export interface SnowLumaHttpClientOptions extends SnowLumaClientOptions {
+  /** OneBot HTTP endpoint. Defaults to http://127.0.0.1:3000/. */
+  baseUrl?: string;
+  /** Custom fetch implementation for tests or non-standard runtimes. */
+  fetch?: typeof fetch;
+  /** Extra headers sent with every request. Authorization is managed by accessToken. */
+  headers?: Record<string, string>;
+}
+
+/** OneBot HTTP client for SnowLuma. */
+export class SnowLumaHttpClient extends SnowLumaApiClient {
+  readonly baseUrl: string;
+  readonly accessToken?: string;
+  readonly requestTimeoutMs: number;
+
+  private readonly fetchImpl: typeof fetch;
+  private readonly headers: Record<string, string>;
+
+  constructor(options: SnowLumaHttpClientOptions = {}) {
+    super();
+    this.baseUrl = options.baseUrl ?? 'http://127.0.0.1:3000/';
+    this.accessToken = options.accessToken;
+    this.requestTimeoutMs = options.requestTimeoutMs ?? 30_000;
+    this.fetchImpl = options.fetch ?? globalThis.fetch;
+    this.headers = options.headers ?? {};
+
+    if (!this.fetchImpl) {
+      throw new SnowLumaConnectionError('No fetch implementation is available');
+    }
+  }
+
+  /** Sends one OneBot action over HTTP and returns the raw response envelope. */
+  override async request<TAction extends SnowLumaAction>(
+    action: TAction,
+    params?: ActionParams<TAction>,
+    options?: RequestOptions,
+  ): Promise<ApiResponse<ActionResult<TAction>>> {
+    const timeoutMs = options?.timeoutMs ?? this.requestTimeoutMs;
+    const abort = createRequestAbortState(timeoutMs, options?.signal);
+
+    try {
+      const response = await this.fetchImpl(this.baseUrl, {
+        method: 'POST',
+        headers: this.createHeaders(),
+        body: JSON.stringify({
+          action,
+          params: toJsonObject(params as JsonObject | undefined),
+          echo: options?.echo,
+        }),
+        signal: abort.signal,
+      });
+
+      const text = await response.text();
+      let parsed: unknown;
+      try {
+        parsed = text ? JSON.parse(text) : null;
+      } catch (error) {
+        throw new SnowLumaParseError(`SnowLuma returned non-JSON HTTP ${response.status}`, { cause: error });
+      }
+
+      const apiResponse = assertApiResponse(parsed) as ApiResponse<ActionResult<TAction>>;
+      return apiResponse;
+    } catch (error) {
+      if (error instanceof SnowLumaTransportError) throw error;
+      if (isAbortError(error) || abort.signal.aborted) {
+        if (abort.isTimedOut()) {
+          throw new SnowLumaTimeoutError(`SnowLuma request timed out after ${timeoutMs}ms`, timeoutMs, { cause: error });
+        }
+        if (abort.isExternallyAborted()) {
+          throw new SnowLumaAbortError('SnowLuma request aborted', { cause: error });
+        }
+      }
+      throw new SnowLumaConnectionError('SnowLuma HTTP request failed', { cause: error });
+    } finally {
+      abort.cleanup();
+    }
+  }
+
+  private createHeaders(): Record<string, string> {
+    const headers: Record<string, string> = {
+      'Content-Type': 'application/json',
+      Accept: 'application/json',
+      ...this.headers,
+    };
+    if (this.accessToken) {
+      headers.Authorization = `Bearer ${this.accessToken}`;
+    }
+    return headers;
+  }
+}
+
+export function createHttpClient(options?: SnowLumaHttpClientOptions): SnowLumaHttpClient {
+  return new SnowLumaHttpClient(options);
+}
diff --git a/packages/sdk/src/client/index.ts b/packages/sdk/src/client/index.ts
new file mode 100644
index 00000000..23a1059f
--- /dev/null
+++ b/packages/sdk/src/client/index.ts
@@ -0,0 +1,12 @@
+export { SnowLumaApiClient } from './api-client';
+export { SnowLumaHttpClient, createHttpClient } from './http-client';
+export { SnowLumaWebSocketClient, createWebSocketClient } from './websocket-client';
+
+export type { SnowLumaHttpClientOptions } from './http-client';
+export type {
+  ReconnectOptions,
+  SnowLumaWebSocketClientOptions,
+  SnowLumaWebSocketEvents,
+  WebSocketCloseInfo,
+  WebSocketConstructor,
+} from './websocket-client';
diff --git a/packages/sdk/src/client/websocket-client.ts b/packages/sdk/src/client/websocket-client.ts
new file mode 100644
index 00000000..89e68867
--- /dev/null
+++ b/packages/sdk/src/client/websocket-client.ts
@@ -0,0 +1,421 @@
+import {
+  SnowLumaAbortError,
+  SnowLumaConnectionError,
+  SnowLumaParseError,
+  SnowLumaTimeoutError,
+} from '../errors';
+import { Emitter } from '../emitter';
+import {
+  createEventContext,
+  isGroupMessageEvent,
+  isMessageEvent,
+  isMetaEvent,
+  isNoticeEvent,
+  isPrivateMessageEvent,
+  isRequestEvent,
+  matchCommand,
+  noticeType,
+  requestType,
+  type CommandHandler,
+  type CommandOptions,
+  type EventHandler,
+  type EventMiddleware,
+  type EventPredicate,
+} from '../events/index';
+import { SnowLumaApiClient, toJsonObject } from './api-client';
+import { raceWithAbort, throwIfAborted } from '../internal/abort';
+import { appendAccessToken, assertApiResponse, createEcho, echoKey, isJsonObject } from '../internal/json';
+import {
+  addSocketListener,
+  closeInfo,
+  normalizeReconnect,
+  rawToString,
+  unwrapEventPayload,
+  unwrapMessagePayload,
+  WEBSOCKET_CLOSED,
+  WEBSOCKET_OPEN,
+} from './websocket-utils';
+import type {
+  ActionParams,
+  ActionResult,
+  ApiResponse,
+  JsonObject,
+  JsonValue,
+  OneBotMessageEvent,
+  OneBotMetaEvent,
+  OneBotNoticeEvent,
+  OneBotRequestEvent,
+  RequestOptions,
+  SnowLumaAction,
+  SnowLumaEvent,
+  WsRole,
+} from '../types/index';
+import type {
+  PendingRequest,
+  ReconnectOptions,
+  SnowLumaWebSocketClientOptions,
+  SnowLumaWebSocketEvents,
+  WebSocketConstructor,
+  WebSocketLike,
+} from './websocket-types';
+
+export type {
+  ReconnectOptions,
+  SnowLumaWebSocketClientOptions,
+  SnowLumaWebSocketEvents,
+  WebSocketCloseInfo,
+  WebSocketConstructor,
+} from './websocket-types';
+
+/** OneBot WebSocket client for SnowLuma APIs and realtime events. */
+export class SnowLumaWebSocketClient extends SnowLumaApiClient {
+  readonly url: string;
+  readonly accessToken?: string;
+  readonly requestTimeoutMs: number;
+  readonly role: WsRole;
+
+  private readonly protocols?: string | string[];
+  private readonly WebSocketCtor: WebSocketConstructor;
+  private readonly reconnect: ReconnectOptions | null;
+  private readonly emitter = new Emitter<SnowLumaWebSocketEvents>();
+  private readonly pending = new Map<string, PendingRequest>();
+  private readonly middlewares: EventMiddleware[] = [];
+  private socket: WebSocketLike | null = null;
+  private connectPromise: Promise<void> | null = null;
+  private reconnectTimer: ReturnType<typeof setTimeout> | null = null;
+  private reconnectAttempts = 0;
+  private closedByUser = false;
+
+  constructor(options: SnowLumaWebSocketClientOptions = {}) {
+    super();
+    this.url = options.url ?? 'ws://127.0.0.1:3001/';
+    this.accessToken = options.accessToken;
+    this.requestTimeoutMs = options.requestTimeoutMs ?? 30_000;
+    this.role = options.role ?? 'Universal';
+    this.protocols = options.protocols;
+    this.WebSocketCtor = options.webSocket ?? globalThis.WebSocket as unknown as WebSocketConstructor;
+    this.reconnect = normalizeReconnect(options.reconnect);
+
+    if (!this.WebSocketCtor) {
+      throw new SnowLumaConnectionError('No WebSocket implementation is available');
+    }
+  }
+
+  /** True when the underlying WebSocket is currently open. */
+  get isConnected(): boolean {
+    return this.socket?.readyState === WEBSOCKET_OPEN;
+  }
+
+  /** Subscribes to low-level client events. Returns an unsubscribe function. */
+  on<TKey extends keyof SnowLumaWebSocketEvents>(
+    event: TKey,
+    listener: (payload: SnowLumaWebSocketEvents[TKey]) => void,
+  ): () => void {
+    return this.emitter.on(event, listener);
+  }
+
+  /** Subscribes to one low-level client event, then automatically unsubscribes. */
+  once<TKey extends keyof SnowLumaWebSocketEvents>(
+    event: TKey,
+    listener: (payload: SnowLumaWebSocketEvents[TKey]) => void,
+  ): () => void {
+    return this.emitter.once(event, listener);
+  }
+
+  /** Removes a previously registered low-level client event listener. */
+  off<TKey extends keyof SnowLumaWebSocketEvents>(
+    event: TKey,
+    listener: (payload: SnowLumaWebSocketEvents[TKey]) => void,
+  ): void {
+    this.emitter.off(event, listener);
+  }
+
+  /** Subscribes to every SnowLuma event packet. */
+  onEvent(listener: (event: SnowLumaEvent) => void): () => void {
+    return this.on('event', listener);
+  }
+
+  /** Adds event middleware to the dispatch pipeline. */
+  use(middleware: EventMiddleware): () => void {
+    this.middlewares.push(middleware);
+    return () => {
+      const index = this.middlewares.indexOf(middleware);
+      if (index >= 0) this.middlewares.splice(index, 1);
+    };
+  }
+
+  /** Runs a handler when a type guard or predicate matches an event. */
+  when<TEvent extends SnowLumaEvent>(
+    predicate: EventPredicate<TEvent>,
+    handler: EventHandler<TEvent>,
+  ): () => void {
+    return this.use(async (event, context, next) => {
+      if (predicate(event)) {
+        await handler(event, context as never);
+      }
+      if (!context.stopped) await next();
+    });
+  }
+
+  onMessage(handler: EventHandler<OneBotMessageEvent>): () => void {
+    return this.when(isMessageEvent, handler);
+  }
+
+  onPrivateMessage(handler: EventHandler<Extract<OneBotMessageEvent, { message_type: 'private' }>>): () => void {
+    return this.when(isPrivateMessageEvent, handler);
+  }
+
+  onGroupMessage(handler: EventHandler<Extract<OneBotMessageEvent, { message_type: 'group' }>>): () => void {
+    return this.when(isGroupMessageEvent, handler);
+  }
+
+  onNotice(handler: EventHandler<OneBotNoticeEvent>): () => void;
+  onNotice(type: string, handler: EventHandler<OneBotNoticeEvent>): () => void;
+  onNotice(typeOrHandler: string | EventHandler<OneBotNoticeEvent>, handler?: EventHandler<OneBotNoticeEvent>): () => void {
+    if (typeof typeOrHandler === 'string') {
+      if (!handler) throw new TypeError('onNotice(type, handler) requires a handler');
+      return this.when(noticeType(typeOrHandler), handler);
+    }
+    return this.when(isNoticeEvent, typeOrHandler);
+  }
+
+  onRequest(handler: EventHandler<OneBotRequestEvent>): () => void;
+  onRequest(type: string, handler: EventHandler<OneBotRequestEvent>): () => void;
+  onRequest(typeOrHandler: string | EventHandler<OneBotRequestEvent>, handler?: EventHandler<OneBotRequestEvent>): () => void {
+    if (typeof typeOrHandler === 'string') {
+      if (!handler) throw new TypeError('onRequest(type, handler) requires a handler');
+      return this.when(requestType(typeOrHandler), handler);
+    }
+    return this.when(isRequestEvent, typeOrHandler);
+  }
+
+  onMetaEvent(handler: EventHandler<OneBotMetaEvent>): () => void {
+    return this.when(isMetaEvent, handler);
+  }
+
+  command(
+    command: string | RegExp,
+    handler: CommandHandler,
+    options?: CommandOptions,
+  ): () => void {
+    return this.onMessage(async (event, context) => {
+      const matched = matchCommand(event, command, options);
+      if (!matched) return;
+      await handler(event, Object.assign(context, { command: matched }), matched);
+    });
+  }
+
+  /** Connects to SnowLuma's OneBot WebSocket endpoint. */
+  async connect(): Promise<void> {
+    if (this.isConnected) return;
+    if (this.connectPromise) return this.connectPromise;
+
+    this.closedByUser = false;
+    this.connectPromise = new Promise((resolve, reject) => {
+      const url = appendAccessToken(this.url, this.accessToken);
+      const socket = new this.WebSocketCtor(url, this.protocols);
+      this.socket = socket;
+
+      const cleanup = [
+        addSocketListener(socket, 'open', () => {
+          cleanup.forEach((off) => off());
+          this.bindSocket(socket);
+          this.reconnectAttempts = 0;
+          this.connectPromise = null;
+          this.emitter.emit('open', undefined);
+          resolve();
+        }),
+        addSocketListener(socket, 'error', (error) => {
+          this.emitter.emit('error', unwrapEventPayload(error));
+        }),
+        addSocketListener(socket, 'close', (...args) => {
+          cleanup.forEach((off) => off());
+          this.connectPromise = null;
+          this.socket = null;
+          reject(new SnowLumaConnectionError('SnowLuma WebSocket closed before opening'));
+          this.handleClose(args);
+        }),
+      ];
+    });
+
+    return this.connectPromise;
+  }
+
+  /** Closes the socket and rejects all pending API requests. */
+  close(code = 1000, reason = 'normal'): void {
+    this.closedByUser = true;
+    if (this.reconnectTimer) {
+      clearTimeout(this.reconnectTimer);
+      this.reconnectTimer = null;
+    }
+    this.rejectPending(new SnowLumaConnectionError('SnowLuma WebSocket client closed'));
+    if (this.socket && this.socket.readyState !== WEBSOCKET_CLOSED) {
+      this.socket.close(code, reason);
+    }
+    this.socket = null;
+    this.connectPromise = null;
+  }
+
+  /** Sends one OneBot action over WebSocket and returns the raw response envelope. */
+  override async request<TAction extends SnowLumaAction>(
+    action: TAction,
+    params?: ActionParams<TAction>,
+    options?: RequestOptions,
+  ): Promise<ApiResponse<ActionResult<TAction>>> {
+    throwIfAborted(options?.signal);
+    await raceWithAbort(this.connect(), options?.signal, 'SnowLuma WebSocket request aborted before connection opened');
+    throwIfAborted(options?.signal);
+
+    const socket = this.socket;
+    if (!socket || socket.readyState !== WEBSOCKET_OPEN) {
+      throw new SnowLumaConnectionError('SnowLuma WebSocket is not open');
+    }
+
+    const echo = options?.echo ?? createEcho();
+    const key = echoKey(echo);
+    const timeoutMs = options?.timeoutMs ?? this.requestTimeoutMs;
+
+    const promise = new Promise<ApiResponse>((resolve, reject) => {
+      let timer: ReturnType<typeof setTimeout> | null = null;
+      let abortListener: (() => void) | undefined;
+      const cleanup = (): void => {
+        if (timer) clearTimeout(timer);
+        if (abortListener) options?.signal?.removeEventListener('abort', abortListener);
+      };
+
+      timer = timeoutMs > 0
+        ? setTimeout(() => {
+          this.pending.delete(key);
+          cleanup();
+          reject(new SnowLumaTimeoutError(`SnowLuma WebSocket request timed out after ${timeoutMs}ms`, timeoutMs));
+        }, timeoutMs)
+        : null;
+
+      abortListener = () => {
+        this.pending.delete(key);
+        cleanup();
+        reject(new SnowLumaAbortError('SnowLuma WebSocket request aborted', { cause: options?.signal?.reason }));
+      };
+      options?.signal?.addEventListener('abort', abortListener, { once: true });
+
+      this.pending.set(key, { resolve, reject, timer, cleanup });
+    });
+
+    try {
+      socket.send(JSON.stringify({
+        action,
+        params: toJsonObject(params as JsonObject | undefined),
+        echo,
+      }));
+    } catch (error) {
+      const pending = this.pending.get(key);
+      pending?.cleanup?.();
+      this.pending.delete(key);
+      throw new SnowLumaConnectionError('Failed to send SnowLuma WebSocket request', { cause: error });
+    }
+
+    return promise as Promise<ApiResponse<ActionResult<TAction>>>;
+  }
+
+  private bindSocket(socket: WebSocketLike): void {
+    addSocketListener(socket, 'message', (...args) => this.handleMessage(args));
+    addSocketListener(socket, 'error', (error) => this.emitter.emit('error', unwrapEventPayload(error)));
+    addSocketListener(socket, 'close', (...args) => this.handleClose(args));
+  }
+
+  private handleMessage(args: unknown[]): void {
+    const raw = unwrapMessagePayload(args[0]);
+    this.emitter.emit('raw', raw);
+
+    let parsed: unknown;
+    try {
+      parsed = JSON.parse(rawToString(raw));
+    } catch (error) {
+      this.emitter.emit('error', new SnowLumaParseError('SnowLuma WebSocket returned non-JSON message', { cause: error }));
+      return;
+    }
+
+    if (isJsonObject(parsed) && parsed.echo !== undefined) {
+      const key = echoKey(parsed.echo as JsonValue);
+      const pending = this.pending.get(key);
+      if (pending) {
+        this.pending.delete(key);
+        pending.cleanup?.();
+        try {
+          const response = assertApiResponse(parsed);
+          pending.resolve(response);
+          this.emitter.emit('response', response);
+        } catch (error) {
+          pending.reject(new SnowLumaParseError('SnowLuma WebSocket response is invalid', { cause: error }));
+        }
+        return;
+      }
+    }
+
+    if (isJsonObject(parsed) && typeof parsed.post_type === 'string') {
+      void this.dispatchEvent(parsed as SnowLumaEvent).catch((error) => {
+        this.emitter.emit('error', error);
+      });
+    }
+  }
+
+  private async dispatchEvent(event: SnowLumaEvent): Promise<void> {
+    const context = createEventContext(event, this);
+    let index = -1;
+
+    const next = async (): Promise<void> => {
+      index += 1;
+      const middleware = this.middlewares[index];
+      if (!middleware || context.stopped) return;
+      await middleware(event, context, next);
+    };
+
+    await next();
+    if (!context.stopped && index >= this.middlewares.length - 1) {
+      this.emitter.emit('event', event);
+    }
+  }
+
+  private handleClose(args: unknown[]): void {
+    const info = closeInfo(args);
+    this.socket = null;
+    this.connectPromise = null;
+    this.rejectPending(new SnowLumaConnectionError('SnowLuma WebSocket closed'));
+    this.emitter.emit('close', info);
+
+    if (!this.closedByUser && this.reconnect) {
+      this.scheduleReconnect();
+    }
+  }
+
+  private scheduleReconnect(): void {
+    if (this.reconnectTimer) return;
+    const reconnect = this.reconnect;
+    if (!reconnect) return;
+    const retries = reconnect.retries ?? Number.POSITIVE_INFINITY;
+    if (this.reconnectAttempts >= retries) return;
+    const minDelay = reconnect.minDelayMs ?? 1000;
+    const maxDelay = reconnect.maxDelayMs ?? 30_000;
+    const delay = Math.min(maxDelay, minDelay * 2 ** this.reconnectAttempts);
+    this.reconnectAttempts += 1;
+    this.reconnectTimer = setTimeout(() => {
+      this.reconnectTimer = null;
+      void this.connect().catch((error) => {
+        this.emitter.emit('error', error);
+        if (!this.closedByUser) this.scheduleReconnect();
+      });
+    }, delay);
+  }
+
+  private rejectPending(error: Error): void {
+    for (const pending of this.pending.values()) {
+      pending.cleanup?.();
+      pending.reject(error);
+    }
+    this.pending.clear();
+  }
+}
+
+export function createWebSocketClient(options?: SnowLumaWebSocketClientOptions): SnowLumaWebSocketClient {
+  return new SnowLumaWebSocketClient(options);
+}
diff --git a/packages/sdk/src/client/websocket-types.ts b/packages/sdk/src/client/websocket-types.ts
new file mode 100644
index 00000000..b50e8054
--- /dev/null
+++ b/packages/sdk/src/client/websocket-types.ts
@@ -0,0 +1,64 @@
+import type {
+  ApiResponse,
+  SnowLumaClientOptions,
+  SnowLumaEvent,
+  WsRole,
+} from '../types/index';
+
+export interface WebSocketLike {
+  readyState: number;
+  send(data: string): void;
+  close(code?: number, reason?: string): void;
+  addEventListener?: (event: string, listener: (...args: unknown[]) => void) => void;
+  removeEventListener?: (event: string, listener: (...args: unknown[]) => void) => void;
+  on?: (event: string, listener: (...args: unknown[]) => void) => void;
+  off?: (event: string, listener: (...args: unknown[]) => void) => void;
+  removeListener?: (event: string, listener: (...args: unknown[]) => void) => void;
+}
+
+export type WebSocketConstructor = new (url: string, protocols?: string | string[]) => WebSocketLike;
+
+/** Reconnect policy for the WebSocket client. */
+export interface ReconnectOptions {
+  /** Maximum reconnect attempts. Omit for unlimited retries. */
+  retries?: number;
+  /** Initial reconnect delay in milliseconds. Defaults to 1000. */
+  minDelayMs?: number;
+  /** Maximum reconnect delay in milliseconds. Defaults to 30000. */
+  maxDelayMs?: number;
+}
+
+/** Options for the WebSocket transport client. */
+export interface SnowLumaWebSocketClientOptions extends SnowLumaClientOptions {
+  /** OneBot WebSocket endpoint. Defaults to ws://127.0.0.1:3001/. */
+  url?: string;
+  /** OneBot WebSocket role advertised by the client. */
+  role?: WsRole;
+  /** Optional WebSocket protocols argument. */
+  protocols?: string | string[];
+  /** Custom WebSocket constructor for Node runtimes or tests. */
+  webSocket?: WebSocketConstructor;
+  /** Enables or configures automatic reconnect after unexpected close. */
+  reconnect?: boolean | ReconnectOptions;
+}
+
+export interface WebSocketCloseInfo {
+  code?: number;
+  reason?: string;
+}
+
+export interface SnowLumaWebSocketEvents {
+  open: undefined;
+  close: WebSocketCloseInfo;
+  error: unknown;
+  event: SnowLumaEvent;
+  response: ApiResponse;
+  raw: unknown;
+}
+
+export interface PendingRequest {
+  resolve: (response: ApiResponse) => void;
+  reject: (error: Error) => void;
+  timer: ReturnType<typeof setTimeout> | null;
+  cleanup?: () => void;
+}
diff --git a/packages/sdk/src/client/websocket-utils.ts b/packages/sdk/src/client/websocket-utils.ts
new file mode 100644
index 00000000..9aceffd8
--- /dev/null
+++ b/packages/sdk/src/client/websocket-utils.ts
@@ -0,0 +1,77 @@
+import { isJsonObject } from '../internal/json';
+import type {
+  ReconnectOptions,
+  WebSocketCloseInfo,
+  WebSocketLike,
+} from './websocket-types';
+
+export const WEBSOCKET_OPEN = 1;
+export const WEBSOCKET_CLOSED = 3;
+
+export function normalizeReconnect(value: boolean | ReconnectOptions | undefined): ReconnectOptions | null {
+  if (!value) return null;
+  if (value === true) return {};
+  return value;
+}
+
+export function addSocketListener(
+  socket: WebSocketLike,
+  event: string,
+  listener: (...args: unknown[]) => void,
+): () => void {
+  if (socket.addEventListener) {
+    socket.addEventListener(event, listener);
+    return () => socket.removeEventListener?.(event, listener);
+  }
+  if (socket.on) {
+    socket.on(event, listener);
+    return () => {
+      if (socket.off) socket.off(event, listener);
+      else socket.removeListener?.(event, listener);
+    };
+  }
+  return () => undefined;
+}
+
+export function unwrapMessagePayload(value: unknown): unknown {
+  if (isJsonObject(value) && 'data' in value) {
+    return value.data;
+  }
+  return value;
+}
+
+export function unwrapEventPayload(value: unknown): unknown {
+  if (isJsonObject(value) && 'error' in value) {
+    return value.error;
+  }
+  return value;
+}
+
+export function rawToString(value: unknown): string {
+  if (typeof value === 'string') return value;
+  if (value instanceof ArrayBuffer) return new TextDecoder().decode(value);
+  if (ArrayBuffer.isView(value)) {
+    return new TextDecoder().decode(value);
+  }
+  if (value instanceof Blob) {
+    throw new Error('Blob WebSocket messages are not supported synchronously');
+  }
+  if (value && typeof value === 'object' && 'toString' in value && typeof value.toString === 'function') {
+    return value.toString();
+  }
+  return String(value);
+}
+
+export function closeInfo(args: unknown[]): WebSocketCloseInfo {
+  const first = args[0];
+  if (isJsonObject(first)) {
+    return {
+      code: typeof first.code === 'number' ? first.code : undefined,
+      reason: typeof first.reason === 'string' ? first.reason : undefined,
+    };
+  }
+  return {
+    code: typeof args[0] === 'number' ? args[0] : undefined,
+    reason: typeof args[1] === 'string' ? args[1] : undefined,
+  };
+}
diff --git a/packages/sdk/src/emitter.ts b/packages/sdk/src/emitter.ts
new file mode 100644
index 00000000..6fa87660
--- /dev/null
+++ b/packages/sdk/src/emitter.ts
@@ -0,0 +1,39 @@
+type Listener<TPayload> = (payload: TPayload) => void;
+
+export class Emitter<TEvents extends object> {
+  private readonly listeners = new Map<keyof TEvents, Set<Listener<never>>>();
+
+  on<TKey extends keyof TEvents>(event: TKey, listener: Listener<TEvents[TKey]>): () => void {
+    let set = this.listeners.get(event);
+    if (!set) {
+      set = new Set();
+      this.listeners.set(event, set);
+    }
+    set.add(listener as Listener<never>);
+    return () => this.off(event, listener);
+  }
+
+  once<TKey extends keyof TEvents>(event: TKey, listener: Listener<TEvents[TKey]>): () => void {
+    const off = this.on(event, (payload) => {
+      off();
+      listener(payload);
+    });
+    return off;
+  }
+
+  off<TKey extends keyof TEvents>(event: TKey, listener: Listener<TEvents[TKey]>): void {
+    this.listeners.get(event)?.delete(listener as Listener<never>);
+  }
+
+  emit<TKey extends keyof TEvents>(event: TKey, payload: TEvents[TKey]): void {
+    const set = this.listeners.get(event);
+    if (!set) return;
+    for (const listener of [...set]) {
+      listener(payload as never);
+    }
+  }
+
+  clear(): void {
+    this.listeners.clear();
+  }
+}
diff --git a/packages/sdk/src/errors.ts b/packages/sdk/src/errors.ts
new file mode 100644
index 00000000..cb6f16d4
--- /dev/null
+++ b/packages/sdk/src/errors.ts
@@ -0,0 +1,83 @@
+import type { ApiResponse } from './types/index';
+
+/** Base error for every exception intentionally thrown by the SnowLuma SDK. */
+export class SnowLumaError extends Error {
+  constructor(message: string, options?: ErrorOptions) {
+    super(message, options);
+    this.name = 'SnowLumaError';
+  }
+}
+
+/** Transport-layer failures before a valid OneBot API response is available. */
+export class SnowLumaTransportError extends SnowLumaError {
+  constructor(message: string, options?: ErrorOptions) {
+    super(message, options);
+    this.name = 'SnowLumaTransportError';
+  }
+}
+
+/** The request was cancelled by the caller's AbortSignal. */
+export class SnowLumaAbortError extends SnowLumaTransportError {
+  constructor(message = 'SnowLuma request aborted', options?: ErrorOptions) {
+    super(message, options);
+    this.name = 'SnowLumaAbortError';
+  }
+}
+
+/** The request exceeded the configured timeout. */
+export class SnowLumaTimeoutError extends SnowLumaTransportError {
+  readonly timeoutMs: number;
+
+  constructor(message: string, timeoutMs: number, options?: ErrorOptions) {
+    super(message, options);
+    this.name = 'SnowLumaTimeoutError';
+    this.timeoutMs = timeoutMs;
+  }
+}
+
+/** The SDK could not establish or keep a connection to SnowLuma. */
+export class SnowLumaConnectionError extends SnowLumaTransportError {
+  constructor(message: string, options?: ErrorOptions) {
+    super(message, options);
+    this.name = 'SnowLumaConnectionError';
+  }
+}
+
+/** SnowLuma returned a payload that could not be parsed as the expected protocol shape. */
+export class SnowLumaParseError extends SnowLumaTransportError {
+  constructor(message: string, options?: ErrorOptions) {
+    super(message, options);
+    this.name = 'SnowLumaParseError';
+  }
+}
+
+/** A OneBot API response with status failed or a non-zero retcode. */
+export class SnowLumaApiError<TData = unknown> extends SnowLumaError {
+  readonly response: ApiResponse<TData>;
+  readonly retcode: number;
+  readonly wording?: string;
+
+  constructor(response: ApiResponse<TData>) {
+    super(response.wording || `SnowLuma API failed with retcode ${response.retcode}`);
+    this.name = 'SnowLumaApiError';
+    this.response = response;
+    this.retcode = response.retcode;
+    this.wording = response.wording;
+  }
+}
+
+/** Authentication or authorization failure returned by SnowLuma. */
+export class SnowLumaAuthError<TData = unknown> extends SnowLumaApiError<TData> {
+  constructor(response: ApiResponse<TData>) {
+    super(response);
+    this.name = 'SnowLumaAuthError';
+  }
+}
+
+export function createSnowLumaApiError<TData>(response: ApiResponse<TData>): SnowLumaApiError<TData> {
+  return isAuthFailure(response) ? new SnowLumaAuthError(response) : new SnowLumaApiError(response);
+}
+
+function isAuthFailure(response: ApiResponse<unknown>): boolean {
+  return response.retcode === 1401 || response.retcode === 401 || response.retcode === 403;
+}
diff --git a/packages/sdk/src/events/command.ts b/packages/sdk/src/events/command.ts
new file mode 100644
index 00000000..232135f0
--- /dev/null
+++ b/packages/sdk/src/events/command.ts
@@ -0,0 +1,55 @@
+import type { OneBotMessageEvent } from '../types/index';
+import type { CommandMatch, CommandOptions } from './types';
+
+export function matchCommand(
+  event: OneBotMessageEvent,
+  command: string | RegExp,
+  options: CommandOptions = {},
+): CommandMatch | null {
+  const trim = options.trim ?? true;
+  const raw = trim ? event.raw_message.trim() : event.raw_message;
+  const prefixes = normalizePrefixes(options.prefixes ?? '/');
+
+  for (const prefix of prefixes) {
+    if (prefix && !raw.startsWith(prefix)) continue;
+
+    const text = prefix ? raw.slice(prefix.length).trimStart() : raw;
+    if (!text) continue;
+
+    if (command instanceof RegExp) {
+      const match = text.match(command);
+      if (!match || match.index !== 0) continue;
+      const matchedText = match[0] ?? '';
+      const rest = text.slice(matchedText.length).trim();
+      return {
+        command: matchedText,
+        text,
+        args: rest ? rest.split(/\s+/) : [],
+        rest,
+        prefix,
+        match,
+      };
+    }
+
+    const [head = '', ...args] = text.split(/\s+/);
+    const matches = options.caseSensitive
+      ? head === command
+      : head.toLowerCase() === command.toLowerCase();
+    if (!matches) continue;
+
+    return {
+      command: head,
+      text,
+      args,
+      rest: text.slice(head.length).trim(),
+      prefix,
+      match: null,
+    };
+  }
+
+  return null;
+}
+
+function normalizePrefixes(prefixes: string | string[]): string[] {
+  return Array.isArray(prefixes) ? prefixes : [prefixes];
+}
diff --git a/packages/sdk/src/events/context.ts b/packages/sdk/src/events/context.ts
new file mode 100644
index 00000000..a34d8817
--- /dev/null
+++ b/packages/sdk/src/events/context.ts
@@ -0,0 +1,73 @@
+import type { SnowLumaApiClient } from '../client/api-client';
+import type { SnowLumaEvent } from '../types/index';
+import { isGroupMessageEvent, isPrivateMessageEvent, isRequestEvent } from './guards';
+import type { SnowLumaEventContext } from './types';
+
+/** Creates the helper context object used by WebSocket event handlers. */
+export function createEventContext<TEvent extends SnowLumaEvent>(
+  event: TEvent,
+  client: SnowLumaApiClient,
+): SnowLumaEventContext<TEvent> {
+  let stopped = false;
+
+  const context: SnowLumaEventContext<TEvent> = {
+    event,
+    client,
+    get stopped() {
+      return stopped;
+    },
+    stopPropagation() {
+      stopped = true;
+    },
+    async reply(message, options) {
+      if (isGroupMessageEvent(event)) {
+        return client.sendGroupMessage(event.group_id, message, options);
+      }
+      if (isPrivateMessageEvent(event)) {
+        return client.sendPrivateMessage(event.user_id, message, options);
+      }
+      throw new Error('reply() is only available for message events');
+    },
+    async approve(options) {
+      if (!isRequestEvent(event)) {
+        throw new Error('approve() is only available for request events');
+      }
+      if (event.request_type === 'friend') {
+        return client.setFriendAddRequest(event.flag, true, options);
+      }
+      if (event.request_type === 'group') {
+        return client.setGroupAddRequest(event.flag, {
+          ...options,
+          subType: options?.subType ?? event.sub_type,
+          approve: true,
+        });
+      }
+      throw new Error(`approve() does not support request_type=${event.request_type}`);
+    },
+    async reject(reason, options) {
+      if (!isRequestEvent(event)) {
+        throw new Error('reject() is only available for request events');
+      }
+      if (event.request_type === 'friend') {
+        return client.setFriendAddRequest(event.flag, false, options);
+      }
+      if (event.request_type === 'group') {
+        return client.setGroupAddRequest(event.flag, {
+          ...options,
+          subType: options?.subType ?? event.sub_type,
+          approve: false,
+          reason: reason ?? options?.reason,
+        });
+      }
+      throw new Error(`reject() does not support request_type=${event.request_type}`);
+    },
+    async quickOperation(operation, options) {
+      return client.raw('.handle_quick_operation', {
+        context: event,
+        operation,
+      }, options);
+    },
+  };
+
+  return context;
+}
diff --git a/packages/sdk/src/events/guards.ts b/packages/sdk/src/events/guards.ts
new file mode 100644
index 00000000..590becf4
--- /dev/null
+++ b/packages/sdk/src/events/guards.ts
@@ -0,0 +1,43 @@
+import type {
+  OneBotGroupMessageEvent,
+  OneBotMessageEvent,
+  OneBotMetaEvent,
+  OneBotNoticeEvent,
+  OneBotPrivateMessageEvent,
+  OneBotRequestEvent,
+  SnowLumaEvent,
+} from '../types/index';
+import type { EventPredicate } from './types';
+
+export function isMessageEvent(event: SnowLumaEvent): event is OneBotMessageEvent {
+  return (event.post_type === 'message' || event.post_type === 'message_sent')
+    && (event.message_type === 'private' || event.message_type === 'group');
+}
+
+export function isPrivateMessageEvent(event: SnowLumaEvent): event is OneBotPrivateMessageEvent {
+  return isMessageEvent(event) && event.message_type === 'private';
+}
+
+export function isGroupMessageEvent(event: SnowLumaEvent): event is OneBotGroupMessageEvent {
+  return isMessageEvent(event) && event.message_type === 'group';
+}
+
+export function isNoticeEvent(event: SnowLumaEvent): event is OneBotNoticeEvent {
+  return event.post_type === 'notice' && typeof event.notice_type === 'string';
+}
+
+export function isRequestEvent(event: SnowLumaEvent): event is OneBotRequestEvent {
+  return event.post_type === 'request' && typeof event.request_type === 'string' && typeof event.flag === 'string';
+}
+
+export function isMetaEvent(event: SnowLumaEvent): event is OneBotMetaEvent {
+  return event.post_type === 'meta_event' && typeof event.meta_event_type === 'string';
+}
+
+export function noticeType(type: string): EventPredicate<OneBotNoticeEvent> {
+  return (event): event is OneBotNoticeEvent => isNoticeEvent(event) && event.notice_type === type;
+}
+
+export function requestType(type: string): EventPredicate<OneBotRequestEvent> {
+  return (event): event is OneBotRequestEvent => isRequestEvent(event) && event.request_type === type;
+}
diff --git a/packages/sdk/src/events/index.ts b/packages/sdk/src/events/index.ts
new file mode 100644
index 00000000..41a5a1a0
--- /dev/null
+++ b/packages/sdk/src/events/index.ts
@@ -0,0 +1,4 @@
+export * from './types';
+export * from './guards';
+export * from './context';
+export * from './command';
diff --git a/packages/sdk/src/events/types.ts b/packages/sdk/src/events/types.ts
new file mode 100644
index 00000000..e8cd8eee
--- /dev/null
+++ b/packages/sdk/src/events/types.ts
@@ -0,0 +1,73 @@
+import type { SnowLumaApiClient } from '../client/api-client';
+import type {
+  JsonObject,
+  OneBotMessageEvent,
+  OutgoingMessage,
+  RequestOptions,
+  SnowLumaEvent,
+} from '../types/index';
+
+export type MaybePromise<T = void> = T | Promise<T>;
+export type EventNext = () => Promise<void>;
+
+/** Type guard or predicate used by client.when(). */
+export type EventPredicate<TEvent extends SnowLumaEvent = SnowLumaEvent> = (event: SnowLumaEvent) => event is TEvent;
+
+/** Handler for one narrowed SnowLuma event. */
+export type EventHandler<TEvent extends SnowLumaEvent = SnowLumaEvent> = (
+  event: TEvent,
+  context: SnowLumaEventContext<TEvent>,
+) => MaybePromise;
+
+/** Middleware in the WebSocket event dispatch pipeline. */
+export type EventMiddleware = (
+  event: SnowLumaEvent,
+  context: SnowLumaEventContext,
+  next: EventNext,
+) => MaybePromise;
+
+/** Options for accepting or rejecting OneBot request events. */
+export interface RequestDecisionOptions extends RequestOptions {
+  reason?: string;
+  subType?: string;
+}
+
+/** Convenience context passed to event middleware and handlers. */
+export interface SnowLumaEventContext<TEvent extends SnowLumaEvent = SnowLumaEvent> {
+  readonly event: TEvent;
+  readonly client: SnowLumaApiClient;
+  readonly stopped: boolean;
+  /** Prevents subsequent middleware and final onEvent listeners from running. */
+  stopPropagation(): void;
+  /** Replies to private or group message events with the correct API. */
+  reply(message: OutgoingMessage, options?: RequestOptions & { autoEscape?: boolean }): Promise<unknown>;
+  /** Approves a friend or group request event. */
+  approve(options?: RequestDecisionOptions): Promise<unknown>;
+  /** Rejects a friend or group request event. */
+  reject(reason?: string, options?: RequestDecisionOptions): Promise<unknown>;
+  /** Sends OneBot .handle_quick_operation with the current event as context. */
+  quickOperation(operation: JsonObject, options?: RequestOptions): Promise<unknown>;
+}
+
+/** Command matching options for WebSocketClient.command(). */
+export interface CommandOptions {
+  prefixes?: string | string[];
+  trim?: boolean;
+  caseSensitive?: boolean;
+}
+
+/** Parsed command information passed to command handlers. */
+export interface CommandMatch {
+  command: string;
+  text: string;
+  args: string[];
+  rest: string;
+  prefix: string;
+  match: RegExpMatchArray | null;
+}
+
+export type CommandHandler<TEvent extends OneBotMessageEvent = OneBotMessageEvent> = (
+  event: TEvent,
+  context: SnowLumaEventContext<TEvent> & { command: CommandMatch },
+  match: CommandMatch,
+) => MaybePromise;
diff --git a/packages/sdk/src/index.ts b/packages/sdk/src/index.ts
new file mode 100644
index 00000000..347af598
--- /dev/null
+++ b/packages/sdk/src/index.ts
@@ -0,0 +1,88 @@
+export { SNOWLUMA_ACTIONS, isSnowLumaAction } from './actions';
+export { SnowLumaApiClient } from './client/api-client';
+export { SnowLumaHttpClient, createHttpClient } from './client/http-client';
+export { SnowLumaWebSocketClient, createWebSocketClient } from './client/websocket-client';
+export {
+  SnowLumaAbortError,
+  SnowLumaApiError,
+  SnowLumaAuthError,
+  SnowLumaConnectionError,
+  SnowLumaError,
+  SnowLumaParseError,
+  SnowLumaTimeoutError,
+  SnowLumaTransportError,
+  createSnowLumaApiError,
+} from './errors';
+export {
+  MessageChain,
+  at,
+  atAll,
+  br,
+  chain,
+  contact,
+  escapeCqParam,
+  escapeCqText,
+  face,
+  forward,
+  image,
+  json,
+  location,
+  message,
+  music,
+  node,
+  normalizeMessage,
+  parseSegments,
+  poke,
+  raw,
+  record,
+  reply,
+  share,
+  text,
+  toCQString,
+  video,
+  xml,
+  fromCQString,
+} from './messages/index';
+export {
+  createEventContext,
+  isGroupMessageEvent,
+  isMessageEvent,
+  isMetaEvent,
+  isNoticeEvent,
+  isPrivateMessageEvent,
+  isRequestEvent,
+  matchCommand,
+  noticeType,
+  requestType,
+} from './events/index';
+
+export type {
+  SnowLumaKnownAction,
+} from './actions';
+
+export type {
+  SnowLumaHttpClientOptions,
+} from './client/http-client';
+
+export type {
+  ReconnectOptions,
+  SnowLumaWebSocketClientOptions,
+  SnowLumaWebSocketEvents,
+  WebSocketCloseInfo,
+  WebSocketConstructor,
+} from './client/websocket-client';
+
+export type {
+  CommandHandler,
+  CommandMatch,
+  CommandOptions,
+  EventHandler,
+  EventMiddleware,
+  EventNext,
+  EventPredicate,
+  MaybePromise,
+  RequestDecisionOptions,
+  SnowLumaEventContext,
+} from './events/index';
+
+export type * from './types/index';
diff --git a/packages/sdk/src/internal/abort.ts b/packages/sdk/src/internal/abort.ts
new file mode 100644
index 00000000..53273e31
--- /dev/null
+++ b/packages/sdk/src/internal/abort.ts
@@ -0,0 +1,82 @@
+import { SnowLumaAbortError } from '../errors';
+
+export interface RequestAbortState {
+  signal: AbortSignal;
+  cleanup(): void;
+  isTimedOut(): boolean;
+  isExternallyAborted(): boolean;
+}
+
+export function createRequestAbortState(
+  timeoutMs: number,
+  externalSignal?: AbortSignal,
+): RequestAbortState {
+  const controller = new AbortController();
+  let timedOut = false;
+  let externallyAborted = false;
+
+  const onExternalAbort = (): void => {
+    externallyAborted = true;
+    controller.abort(externalSignal?.reason);
+  };
+
+  if (externalSignal?.aborted) {
+    onExternalAbort();
+  } else {
+    externalSignal?.addEventListener('abort', onExternalAbort, { once: true });
+  }
+
+  const timer = timeoutMs > 0
+    ? setTimeout(() => {
+      timedOut = true;
+      controller.abort();
+    }, timeoutMs)
+    : null;
+
+  return {
+    signal: controller.signal,
+    cleanup() {
+      if (timer) clearTimeout(timer);
+      externalSignal?.removeEventListener('abort', onExternalAbort);
+    },
+    isTimedOut() {
+      return timedOut;
+    },
+    isExternallyAborted() {
+      return externallyAborted || externalSignal?.aborted === true;
+    },
+  };
+}
+
+export function throwIfAborted(signal?: AbortSignal, message = 'SnowLuma request aborted'): void {
+  if (signal?.aborted) {
+    throw new SnowLumaAbortError(message, { cause: signal.reason });
+  }
+}
+
+export function isAbortError(error: unknown): boolean {
+  return typeof error === 'object'
+    && error !== null
+    && 'name' in error
+    && (error as { name?: unknown }).name === 'AbortError';
+}
+
+export function raceWithAbort<T>(
+  promise: Promise<T>,
+  signal?: AbortSignal,
+  message = 'SnowLuma request aborted',
+): Promise<T> {
+  if (!signal) return promise;
+  throwIfAborted(signal, message);
+
+  return new Promise<T>((resolve, reject) => {
+    const onAbort = (): void => {
+      reject(new SnowLumaAbortError(message, { cause: signal.reason }));
+    };
+
+    signal.addEventListener('abort', onAbort, { once: true });
+    promise.then(resolve, reject).finally(() => {
+      signal.removeEventListener('abort', onAbort);
+    });
+  });
+}
diff --git a/packages/sdk/src/internal/json.ts b/packages/sdk/src/internal/json.ts
new file mode 100644
index 00000000..5821a1bb
--- /dev/null
+++ b/packages/sdk/src/internal/json.ts
@@ -0,0 +1,64 @@
+import type { ApiResponse, JsonObject, JsonValue } from '../types/index';
+
+export function isJsonObject(value: unknown): value is JsonObject {
+  return typeof value === 'object' && value !== null && !Array.isArray(value);
+}
+
+export function asJsonValue(value: unknown): JsonValue {
+  if (value === null) return null;
+  if (typeof value === 'string' || typeof value === 'number' || typeof value === 'boolean') {
+    return value;
+  }
+  if (Array.isArray(value)) return value.map(asJsonValue);
+  if (isJsonObject(value)) {
+    const out: JsonObject = {};
+    for (const [key, item] of Object.entries(value)) {
+      if (item === undefined) continue;
+      out[key] = asJsonValue(item);
+    }
+    return out;
+  }
+  return String(value);
+}
+
+export function assertApiResponse(value: unknown): ApiResponse {
+  if (!isJsonObject(value)) {
+    throw new Error('response is not a JSON object');
+  }
+
+  const status = value.status === 'ok' ? 'ok' : value.status === 'failed' ? 'failed' : null;
+  if (!status) {
+    throw new Error('response status is missing or invalid');
+  }
+
+  const retcode = typeof value.retcode === 'number' && Number.isFinite(value.retcode)
+    ? value.retcode
+    : status === 'ok' ? 0 : -1;
+
+  return {
+    status,
+    retcode,
+    data: asJsonValue(value.data ?? null),
+    echo: value.echo === undefined ? undefined : asJsonValue(value.echo),
+    wording: typeof value.wording === 'string' ? value.wording : undefined,
+  };
+}
+
+export function createEcho(): string {
+  const random = Math.random().toString(36).slice(2);
+  return `snowluma-sdk:${Date.now().toString(36)}:${random}`;
+}
+
+export function echoKey(value: JsonValue | undefined): string {
+  if (value === undefined) return '';
+  return JSON.stringify(value);
+}
+
+export function appendAccessToken(urlValue: string, accessToken?: string): string {
+  if (!accessToken) return urlValue;
+  const url = new URL(urlValue);
+  if (!url.searchParams.has('access_token')) {
+    url.searchParams.set('access_token', accessToken);
+  }
+  return url.toString();
+}
diff --git a/packages/sdk/src/messages/chain.ts b/packages/sdk/src/messages/chain.ts
new file mode 100644
index 00000000..46600a3b
--- /dev/null
+++ b/packages/sdk/src/messages/chain.ts
@@ -0,0 +1,306 @@
+import { segments } from './segments';
+import { segmentsToCQString } from './cq-format';
+import type {
+  AnyMessageSegment,
+  ContactSegment,
+  ImageSegment,
+  JsonObject,
+  LocationSegment,
+  MessageChainLike,
+  MessageSegment,
+  MusicSegment,
+  OutgoingMessage,
+  RecordSegment,
+  RequestOptions,
+  ShareSegment,
+  VideoSegment,
+  XmlSegment,
+} from '../types/index';
+
+export interface MessageChainSender {
+  sendGroupMessage(groupId: number, message: OutgoingMessage, options?: RequestOptions & { autoEscape?: boolean }): Promise<unknown>;
+  sendPrivateMessage(userId: number, message: OutgoingMessage, options?: RequestOptions & { autoEscape?: boolean }): Promise<unknown>;
+}
+
+const SINGLE_USE_TYPES = new Set(['reply']);
+
+/**
+ * Immutable fluent builder for OneBot message segments.
+ *
+ * The generic state tracks single-use segments such as reply(), so TypeScript
+ * can reject duplicate reply segments in normal chained calls.
+ */
+export class MessageChain<THasReply extends boolean = false> implements MessageChainLike {
+  private readonly replyStateBrand?: THasReply;
+
+  private constructor(
+    private readonly items: AnyMessageSegment[] = [],
+    private readonly used: ReadonlySet<string> = new Set(),
+  ) {}
+
+  static empty(): MessageChain<false> {
+    return new MessageChain<false>();
+  }
+
+  /** Number of segments currently in the chain. */
+  get length(): number {
+    return this.items.length;
+  }
+
+  /** True when no segment has been appended. */
+  get isEmpty(): boolean {
+    return this.items.length === 0;
+  }
+
+  /** Appends a text segment. */
+  text(text = ''): MessageChain<THasReply> {
+    return this.addSegment(segments.text(text));
+  }
+
+  /** Appends a newline text segment. */
+  br(): MessageChain<THasReply> {
+    return this.text('\n');
+  }
+
+  face(id: number | string): MessageChain<THasReply> {
+    return this.addSegment(segments.face(id));
+  }
+
+  /** Mentions a user or everyone in a group. */
+  at(qq: number | 'all', options: { name?: string; uid?: string } = {}): MessageChain<THasReply> {
+    return this.addSegment(segments.at(qq, options));
+  }
+
+  atAll(): MessageChain<THasReply> {
+    return this.at('all');
+  }
+
+  /** Adds a reply segment. A chain can contain at most one reply segment. */
+  reply(this: MessageChain<false>, id: number | string): MessageChain<true> {
+    return this.addSegment(segments.reply(id), 'reply') as MessageChain<true>;
+  }
+
+  /** Appends an image segment from a URL, local path, file id, or base64 URI. */
+  image(file: string, options: Omit<ImageSegment['data'], 'file'> = {}): MessageChain<THasReply> {
+    return this.addSegment(segments.image(file, options));
+  }
+
+  record(file: string, options: Omit<RecordSegment['data'], 'file'> = {}): MessageChain<THasReply> {
+    return this.addSegment(segments.record(file, options));
+  }
+
+  video(file: string, options: Omit<VideoSegment['data'], 'file'> = {}): MessageChain<THasReply> {
+    return this.addSegment(segments.video(file, options));
+  }
+
+  json(data: string | JsonObject): MessageChain<THasReply> {
+    return this.addSegment(segments.json(data));
+  }
+
+  xml(data: string, options: Omit<XmlSegment['data'], 'data'> = {}): MessageChain<THasReply> {
+    return this.addSegment(segments.xml(data, options));
+  }
+
+  poke(type: number | string, id?: number | string): MessageChain<THasReply> {
+    return this.addSegment(segments.poke(type, id));
+  }
+
+  forward(id: string): MessageChain<THasReply> {
+    return this.addSegment(segments.forward(id));
+  }
+
+  node(userId: number, nickname: string, content: OutgoingMessage): MessageChain<THasReply> {
+    return this.addSegment(segments.node(userId, nickname, content));
+  }
+
+  share(options: ShareSegment['data']): MessageChain<THasReply> {
+    return this.addSegment(segments.share(options));
+  }
+
+  music(options: MusicSegment['data']): MessageChain<THasReply> {
+    return this.addSegment(segments.music(options));
+  }
+
+  location(options: LocationSegment['data']): MessageChain<THasReply> {
+    return this.addSegment(segments.location(options));
+  }
+
+  contact(type: ContactSegment['data']['type'], id: number | string): MessageChain<THasReply> {
+    return this.addSegment(segments.contact(type, id));
+  }
+
+  raw<TType extends string, TData extends JsonObject>(type: TType, data: TData): MessageChain<THasReply> {
+    return this.addSegment(segments.raw(type, data), type);
+  }
+
+  /** Appends another outgoing message while preserving single-use segment checks. */
+  append(messageInput: OutgoingMessage): MessageChain<THasReply> {
+    let next: MessageChain<THasReply> = this;
+    const normalized = normalizeMessage(messageInput);
+    if (typeof normalized === 'string') {
+      return next.text(normalized);
+    }
+    for (const segment of normalized) {
+      next = next.addFromSegment(segment);
+    }
+    return next;
+  }
+
+  /** Returns a fresh segment array suitable for OneBot array message format. */
+  build(): AnyMessageSegment[] {
+    return this.toSegments();
+  }
+
+  toArray(): AnyMessageSegment[] {
+    return this.toSegments();
+  }
+
+  toSegments(): AnyMessageSegment[] {
+    return [...this.items];
+  }
+
+  toJSON(): AnyMessageSegment[] {
+    return this.toSegments();
+  }
+
+  toString(): string {
+    return segmentsToCQString(this.items);
+  }
+
+  /** Sends this chain to a group through a compatible SnowLuma client. */
+  sendToGroup(
+    client: MessageChainSender,
+    groupId: number,
+    options?: RequestOptions & { autoEscape?: boolean },
+  ): Promise<unknown> {
+    return client.sendGroupMessage(groupId, this, options);
+  }
+
+  /** Sends this chain to a private chat through a compatible SnowLuma client. */
+  sendToPrivate(
+    client: MessageChainSender,
+    userId: number,
+    options?: RequestOptions & { autoEscape?: boolean },
+  ): Promise<unknown> {
+    return client.sendPrivateMessage(userId, this, options);
+  }
+
+  [Symbol.iterator](): IterableIterator<AnyMessageSegment> {
+    return this.items[Symbol.iterator]();
+  }
+
+  private addFromSegment(segment: AnyMessageSegment): MessageChain<THasReply> {
+    return this.addSegment(segment, segment.type);
+  }
+
+  private addSegment<TNextReply extends boolean = THasReply>(
+    segment: AnyMessageSegment,
+    singleUseType?: string,
+  ): MessageChain<TNextReply> {
+    if (singleUseType && SINGLE_USE_TYPES.has(singleUseType) && this.used.has(singleUseType)) {
+      throw new Error(`Message segment "${singleUseType}" can only appear once in a chain`);
+    }
+
+    const nextUsed = new Set(this.used);
+    if (singleUseType && SINGLE_USE_TYPES.has(singleUseType)) {
+      nextUsed.add(singleUseType);
+    }
+    return new MessageChain<TNextReply>([...this.items, segment], nextUsed);
+  }
+}
+
+export function chain(): MessageChain<false> {
+  return MessageChain.empty();
+}
+
+/** Starts a message chain with a text segment. */
+export function text(value = ''): MessageChain<false> {
+  return chain().text(value);
+}
+
+export function br(): MessageChain<false> {
+  return chain().br();
+}
+
+export function face(id: number | string): MessageChain<false> {
+  return chain().face(id);
+}
+
+export function at(qq: number | 'all', options: { name?: string; uid?: string } = {}): MessageChain<false> {
+  return chain().at(qq, options);
+}
+
+export function atAll(): MessageChain<false> {
+  return chain().atAll();
+}
+
+export function reply(id: number | string): MessageChain<true> {
+  return chain().reply(id);
+}
+
+/** Starts a message chain with an image segment. */
+export function image(file: string, options: Omit<ImageSegment['data'], 'file'> = {}): MessageChain<false> {
+  return chain().image(file, options);
+}
+
+export function record(file: string, options: Omit<RecordSegment['data'], 'file'> = {}): MessageChain<false> {
+  return chain().record(file, options);
+}
+
+export function video(file: string, options: Omit<VideoSegment['data'], 'file'> = {}): MessageChain<false> {
+  return chain().video(file, options);
+}
+
+export function json(data: string | JsonObject): MessageChain<false> {
+  return chain().json(data);
+}
+
+export function xml(data: string, options: Omit<XmlSegment['data'], 'data'> = {}): MessageChain<false> {
+  return chain().xml(data, options);
+}
+
+export function poke(type: number | string, id?: number | string): MessageChain<false> {
+  return chain().poke(type, id);
+}
+
+export function forward(id: string): MessageChain<false> {
+  return chain().forward(id);
+}
+
+export function node(userId: number, nickname: string, content: OutgoingMessage): MessageChain<false> {
+  return chain().node(userId, nickname, content);
+}
+
+export function share(options: ShareSegment['data']): MessageChain<false> {
+  return chain().share(options);
+}
+
+export function music(options: MusicSegment['data']): MessageChain<false> {
+  return chain().music(options);
+}
+
+export function location(options: LocationSegment['data']): MessageChain<false> {
+  return chain().location(options);
+}
+
+export function contact(type: ContactSegment['data']['type'], id: number | string): MessageChain<false> {
+  return chain().contact(type, id);
+}
+
+export function raw<TType extends string, TData extends JsonObject>(type: TType, data: TData): MessageChain<false> {
+  return chain().raw(type, data);
+}
+
+/** Normalizes a string, segment, segment array, or MessageChain into OneBot output. */
+export function normalizeMessage(input: OutgoingMessage): string | AnyMessageSegment[] {
+  if (typeof input === 'string') return input;
+  if (isMessageChainLike(input)) return input.toSegments();
+  return Array.isArray(input) ? input : [input];
+}
+
+function isMessageChainLike(value: unknown): value is MessageChainLike {
+  return typeof value === 'object'
+    && value !== null
+    && 'toSegments' in value
+    && typeof value.toSegments === 'function';
+}
diff --git a/packages/sdk/src/messages/cq-format.ts b/packages/sdk/src/messages/cq-format.ts
new file mode 100644
index 00000000..af24fd04
--- /dev/null
+++ b/packages/sdk/src/messages/cq-format.ts
@@ -0,0 +1,29 @@
+import type { KnownMessageSegment, MessageSegment } from '../types/index';
+
+export function escapeCqText(text: string): string {
+  return text
+    .replace(/&/g, '&amp;')
+    .replace(/\[/g, '&#91;')
+    .replace(/\]/g, '&#93;');
+}
+
+export function escapeCqParam(text: string): string {
+  return escapeCqText(text).replace(/,/g, '&#44;');
+}
+
+export function segmentsToCQString(segments: Array<KnownMessageSegment | MessageSegment>): string {
+  return segments.map(segmentToCq).join('');
+}
+
+function segmentToCq(segment: KnownMessageSegment | MessageSegment): string {
+  if (segment.type === 'text') {
+    return escapeCqText(String(segment.data.text ?? ''));
+  }
+
+  const params = Object.entries(segment.data)
+    .filter(([, value]) => value !== undefined && value !== null)
+    .map(([key, value]) => `${key}=${escapeCqParam(String(value))}`)
+    .join(',');
+
+  return params ? `[CQ:${segment.type},${params}]` : `[CQ:${segment.type}]`;
+}
diff --git a/packages/sdk/src/messages/cq.ts b/packages/sdk/src/messages/cq.ts
new file mode 100644
index 00000000..0e47ecba
--- /dev/null
+++ b/packages/sdk/src/messages/cq.ts
@@ -0,0 +1,105 @@
+import { normalizeMessage, chain } from './chain';
+import { escapeCqText, segmentsToCQString } from './cq-format';
+import { segments } from './segments';
+import type { AnyMessageSegment, OutgoingMessage } from '../types/index';
+
+const CQ_REGEX = /\[CQ:([a-zA-Z0-9_.-]+)(?:,([^\]]*))?\]/g;
+
+export function toCQString(input: OutgoingMessage): string {
+  if (typeof input === 'string') return escapeCqText(input);
+  const normalized = normalizeMessage(input);
+  return typeof normalized === 'string'
+    ? escapeCqText(normalized)
+    : segmentsToCQString(normalized);
+}
+
+export function fromCQString(input: string) {
+  let current = chain();
+  let lastIndex = 0;
+
+  for (const match of input.matchAll(CQ_REGEX)) {
+    const index = match.index ?? 0;
+    if (index > lastIndex) {
+      const textValue = cqUnescape(input.slice(lastIndex, index));
+      if (textValue) current = current.text(textValue);
+    }
+
+    const segment = segmentFromCq(match[1] ?? '', parseCQParams(match[2] ?? ''));
+    if (segment) current = current.append(segment);
+    lastIndex = index + match[0].length;
+  }
+
+  if (lastIndex < input.length) {
+    const textValue = cqUnescape(input.slice(lastIndex));
+    if (textValue) current = current.text(textValue);
+  }
+
+  return current;
+}
+
+export function parseSegments(input: string): AnyMessageSegment[] {
+  return fromCQString(input).toSegments();
+}
+
+function parseCQParams(raw: string): Record<string, string> {
+  const params: Record<string, string> = {};
+  if (!raw) return params;
+
+  for (const pair of raw.split(',')) {
+    const eq = pair.indexOf('=');
+    if (eq <= 0) continue;
+    params[pair.slice(0, eq)] = cqUnescapeParam(pair.slice(eq + 1));
+  }
+
+  return params;
+}
+
+function cqUnescape(text: string): string {
+  return text
+    .replace(/&#91;/g, '[')
+    .replace(/&#93;/g, ']')
+    .replace(/&amp;/g, '&');
+}
+
+function cqUnescapeParam(text: string): string {
+  return cqUnescape(text).replace(/&#44;/g, ',');
+}
+
+function segmentFromCq(type: string, data: Record<string, string>): AnyMessageSegment | null {
+  switch (type) {
+    case 'text':
+      return segments.text(data.text ?? '');
+    case 'face':
+      return segments.face(data.id ?? '0');
+    case 'at':
+      if (data.qq === 'all') return segments.at('all');
+      {
+        const qq = Number(data.qq);
+        return Number.isFinite(qq) && qq > 0
+          ? segments.at(qq, { name: data.name, uid: data.uid })
+          : segments.raw(type, data);
+      }
+    case 'reply':
+      return segments.reply(data.id ?? '0');
+    case 'image':
+      return segments.image(data.file ?? data.url ?? '', {
+        url: data.url,
+        type: data.type === 'flash' ? 'flash' : undefined,
+        summary: data.summary,
+      });
+    case 'record':
+      return segments.record(data.file ?? data.url ?? '', { url: data.url });
+    case 'video':
+      return segments.video(data.file ?? data.url ?? '', { url: data.url, thumb: data.thumb });
+    case 'json':
+      return segments.json(data.data ?? '');
+    case 'xml':
+      return segments.xml(data.data ?? '', { id: data.id });
+    case 'poke':
+      return segments.poke(data.type ?? data.id ?? '0', data.id);
+    case 'forward':
+      return segments.forward(data.id ?? data.res_id ?? data.forward_id ?? '');
+    default:
+      return segments.raw(type, data);
+  }
+}
diff --git a/packages/sdk/src/messages/index.ts b/packages/sdk/src/messages/index.ts
new file mode 100644
index 00000000..ef0a75aa
--- /dev/null
+++ b/packages/sdk/src/messages/index.ts
@@ -0,0 +1,33 @@
+import { segments } from './segments';
+
+export { MessageChain } from './chain';
+export {
+  at,
+  atAll,
+  br,
+  chain,
+  contact,
+  face,
+  forward,
+  image,
+  json,
+  location,
+  music,
+  node,
+  normalizeMessage,
+  poke,
+  raw,
+  record,
+  reply,
+  share,
+  text,
+  video,
+  xml,
+} from './chain';
+export { escapeCqParam, escapeCqText } from './cq-format';
+export { fromCQString, parseSegments, toCQString } from './cq';
+export { segments };
+
+export const message = {
+  ...segments,
+};
diff --git a/packages/sdk/src/messages/segments.ts b/packages/sdk/src/messages/segments.ts
new file mode 100644
index 00000000..ad3ac16b
--- /dev/null
+++ b/packages/sdk/src/messages/segments.ts
@@ -0,0 +1,100 @@
+import type {
+  AtSegment,
+  ContactSegment,
+  FaceSegment,
+  ForwardSegment,
+  ImageSegment,
+  JsonObject,
+  JsonSegment,
+  LocationSegment,
+  MessageSegment,
+  MusicSegment,
+  NodeSegment,
+  OutgoingMessage,
+  PokeSegment,
+  RecordSegment,
+  ReplySegment,
+  ShareSegment,
+  TextSegment,
+  VideoSegment,
+  XmlSegment,
+} from '../types/index';
+
+function seg<TType extends string, TData extends Record<string, unknown>>(type: TType, data: TData): MessageSegment<TType, TData> {
+  return { type, data };
+}
+
+export const segments = {
+  text(text: string): TextSegment {
+    return seg('text', { text });
+  },
+
+  face(id: number | string): FaceSegment {
+    return seg('face', { id: String(id) });
+  },
+
+  at(qq: number | 'all', options: { name?: string; uid?: string } = {}): AtSegment {
+    const data: AtSegment['data'] = { qq: String(qq) };
+    if (options.name) data.name = options.name;
+    if (options.uid) data.uid = options.uid;
+    return seg('at', data);
+  },
+
+  reply(id: number | string): ReplySegment {
+    return seg('reply', { id: String(id) });
+  },
+
+  image(file: string, options: Omit<ImageSegment['data'], 'file'> = {}): ImageSegment {
+    return seg('image', { file, ...options });
+  },
+
+  record(file: string, options: Omit<RecordSegment['data'], 'file'> = {}): RecordSegment {
+    return seg('record', { file, ...options });
+  },
+
+  video(file: string, options: Omit<VideoSegment['data'], 'file'> = {}): VideoSegment {
+    return seg('video', { file, ...options });
+  },
+
+  json(data: string | JsonObject): JsonSegment {
+    return seg('json', { data: typeof data === 'string' ? data : JSON.stringify(data) });
+  },
+
+  xml(data: string, options: Omit<XmlSegment['data'], 'data'> = {}): XmlSegment {
+    return seg('xml', { data, ...options });
+  },
+
+  poke(type: number | string, id?: number | string): PokeSegment {
+    const data: PokeSegment['data'] = { type };
+    if (id !== undefined) data.id = id;
+    return seg('poke', data);
+  },
+
+  forward(id: string): ForwardSegment {
+    return seg('forward', { id, res_id: id, forward_id: id });
+  },
+
+  node(userId: number, nickname: string, content: OutgoingMessage): NodeSegment {
+    return seg('node', { user_id: userId, nickname, content });
+  },
+
+  share(options: ShareSegment['data']): ShareSegment {
+    return seg('share', options);
+  },
+
+  music(options: MusicSegment['data']): MusicSegment {
+    return seg('music', options);
+  },
+
+  location(options: LocationSegment['data']): LocationSegment {
+    return seg('location', options);
+  },
+
+  contact(type: ContactSegment['data']['type'], id: number | string): ContactSegment {
+    return seg('contact', { type, id });
+  },
+
+  raw<TType extends string, TData extends JsonObject>(type: TType, data: TData): MessageSegment<TType, TData> {
+    return seg(type, data);
+  },
+};
diff --git a/packages/sdk/src/types/actions.ts b/packages/sdk/src/types/actions.ts
new file mode 100644
index 00000000..7ba67b99
--- /dev/null
+++ b/packages/sdk/src/types/actions.ts
@@ -0,0 +1,208 @@
+import type { JsonArray, JsonObject, JsonValue } from './json';
+import type {
+  CreateGroupFileFolderParams,
+  DeleteFriendParams,
+  DeleteGroupFileFolderParams,
+  DeleteGroupFileParams,
+  DomainParams,
+  DownloadFileParams,
+  ForwardMessageParams,
+  FriendPokeParams,
+  GetForwardMsgParams,
+  GetFriendMessageHistoryParams,
+  GetGroupFilesParams,
+  GetGroupFileUrlParams,
+  GetGroupHonorInfoParams,
+  GetGroupInfoParams,
+  GetGroupListParams,
+  GetGroupMemberInfoParams,
+  GetGroupMemberListParams,
+  GetGroupMessageHistoryParams,
+  GetMediaParams,
+  GetPrivateFileUrlParams,
+  GroupForwardMessageParams,
+  GroupIdParams,
+  GroupNoticeParams,
+  GroupPokeParams,
+  MarkGroupMsgAsReadParams,
+  MarkMsgAsReadParams,
+  MarkPrivateMsgAsReadParams,
+  MessageIdParams,
+  MoveGroupFileParams,
+  PrivateForwardMessageParams,
+  RenameGroupFileFolderParams,
+  SendGroupMsgParams,
+  SendLikeParams,
+  SendMsgParams,
+  SendPokeParams,
+  SendPrivateMsgParams,
+  SetFriendAddRequestParams,
+  SetFriendRemarkParams,
+  SetGroupAddRequestParams,
+  SetGroupAdminParams,
+  SetGroupBanParams,
+  SetGroupCardParams,
+  SetGroupKickParams,
+  SetGroupNameParams,
+  SetGroupReactionParams,
+  SetGroupSpecialTitleParams,
+  SetGroupWholeBanParams,
+  SetMsgEmojiLikeParams,
+  SetOnlineStatusParams,
+  SetQqProfileParams,
+  UploadGroupFileParams,
+  UploadPrivateFileParams,
+  UserIdParams,
+  QuickOperationParams,
+} from './params';
+import type {
+  CapabilityInfo,
+  ClientKeyInfo,
+  CookieInfo,
+  CredentialsInfo,
+  CsrfInfo,
+  DownloadFileResult,
+  EmptyData,
+  ForwardMessageResult,
+  FriendMessageHistory,
+  GroupAtAllRemainInfo,
+  GroupFileSystemInfo,
+  GroupFileUrl,
+  GroupMessageHistory,
+  LoginInfo,
+  MediaInfo,
+  OnlineClientsInfo,
+  PrivateFileUrl,
+  SendMessageResult,
+  StatusInfo,
+  UploadForwardResult,
+  UrlSafetyInfo,
+  VersionInfo,
+} from './results';
+
+export type ActionData = JsonValue;
+
+export interface SnowLumaActionMap {
+  get_login_info: { params: JsonObject; data: LoginInfo };
+  get_status: { params: JsonObject; data: StatusInfo };
+  get_version_info: { params: JsonObject; data: VersionInfo };
+  can_send_image: { params: JsonObject; data: CapabilityInfo };
+  can_send_record: { params: JsonObject; data: CapabilityInfo };
+  send_msg: { params: SendMsgParams; data: SendMessageResult };
+  send_private_msg: { params: SendPrivateMsgParams; data: SendMessageResult };
+  send_group_msg: { params: SendGroupMsgParams; data: SendMessageResult };
+  get_msg: { params: MessageIdParams; data: JsonObject };
+  delete_msg: { params: MessageIdParams; data: EmptyData };
+  get_friend_list: { params: JsonObject; data: JsonObject[] };
+  get_stranger_info: { params: UserIdParams; data: JsonObject };
+  delete_friend: { params: DeleteFriendParams; data: EmptyData };
+  get_group_list: { params: GetGroupListParams; data: JsonObject[] };
+  get_group_info: { params: GetGroupInfoParams; data: JsonObject };
+  get_group_member_list: { params: GetGroupMemberListParams; data: JsonObject[] };
+  get_group_member_info: { params: GetGroupMemberInfoParams; data: JsonObject };
+  get_group_honor_info: { params: GetGroupHonorInfoParams; data: JsonValue };
+  get_group_system_msg: { params: JsonObject; data: JsonObject[] };
+  set_group_kick: { params: SetGroupKickParams; data: EmptyData };
+  set_group_ban: { params: SetGroupBanParams; data: EmptyData };
+  set_group_whole_ban: { params: SetGroupWholeBanParams; data: EmptyData };
+  set_group_admin: { params: SetGroupAdminParams; data: EmptyData };
+  set_group_card: { params: SetGroupCardParams; data: EmptyData };
+  set_group_name: { params: SetGroupNameParams; data: EmptyData };
+  set_group_leave: { params: GroupIdParams; data: EmptyData };
+  set_group_special_title: { params: SetGroupSpecialTitleParams; data: EmptyData };
+  set_group_anonymous: { params: JsonObject; data: EmptyData };
+  set_group_anonymous_ban: { params: JsonObject; data: EmptyData };
+  set_group_portrait: { params: JsonObject; data: EmptyData };
+  upload_group_file: { params: UploadGroupFileParams; data: { file_id: string | null } };
+  upload_private_file: { params: UploadPrivateFileParams; data: { file_id: string | null } };
+  get_group_file_url: { params: GetGroupFileUrlParams; data: GroupFileUrl };
+  get_group_root_files: { params: GroupIdParams; data: JsonObject };
+  get_group_files_by_folder: { params: GetGroupFilesParams; data: JsonObject };
+  delete_group_file: { params: DeleteGroupFileParams; data: EmptyData };
+  move_group_file: { params: MoveGroupFileParams; data: EmptyData };
+  create_group_file_folder: { params: CreateGroupFileFolderParams; data: EmptyData };
+  delete_group_file_folder: { params: DeleteGroupFileFolderParams; data: EmptyData };
+  rename_group_file_folder: { params: RenameGroupFileFolderParams; data: EmptyData };
+  get_private_file_url: { params: GetPrivateFileUrlParams; data: PrivateFileUrl };
+  set_friend_add_request: { params: SetFriendAddRequestParams; data: EmptyData };
+  set_group_add_request: { params: SetGroupAddRequestParams; data: EmptyData };
+  send_like: { params: SendLikeParams; data: EmptyData };
+  friend_poke: { params: FriendPokeParams; data: EmptyData };
+  group_poke: { params: GroupPokeParams; data: EmptyData };
+  send_poke: { params: SendPokeParams; data: EmptyData };
+  set_essence_msg: { params: MessageIdParams; data: EmptyData };
+  delete_essence_msg: { params: MessageIdParams; data: EmptyData };
+  get_essence_msg_list: { params: GroupIdParams; data: JsonArray };
+  set_group_reaction: { params: SetGroupReactionParams; data: EmptyData };
+  get_group_msg_history: { params: GetGroupMessageHistoryParams; data: GroupMessageHistory };
+  get_friend_msg_history: { params: GetFriendMessageHistoryParams; data: FriendMessageHistory };
+  mark_group_msg_as_read: { params: MarkGroupMsgAsReadParams; data: EmptyData };
+  mark_private_msg_as_read: { params: MarkPrivateMsgAsReadParams; data: EmptyData };
+  mark_msg_as_read: { params: MarkMsgAsReadParams; data: EmptyData };
+  get_rkey: { params: JsonObject; data: JsonObject[] };
+  ocr_image: { params: JsonObject; data: JsonValue };
+  '.ocr_image': { params: JsonObject; data: JsonValue };
+  _send_group_notice: { params: GroupNoticeParams; data: EmptyData };
+  _get_group_notice: { params: GroupIdParams; data: JsonArray };
+  _del_group_notice: { params: JsonObject; data: EmptyData };
+  upload_forward_msg: { params: ForwardMessageParams; data: UploadForwardResult };
+  upload_foward_msg: { params: ForwardMessageParams; data: UploadForwardResult };
+  send_forward_msg: { params: ForwardMessageParams; data: ForwardMessageResult };
+  send_group_forward_msg: { params: GroupForwardMessageParams; data: ForwardMessageResult };
+  send_private_forward_msg: { params: PrivateForwardMessageParams; data: ForwardMessageResult };
+  get_forward_msg: { params: GetForwardMsgParams; data: { messages: JsonObject[] } };
+  get_image: { params: GetMediaParams; data: MediaInfo };
+  get_record: { params: GetMediaParams; data: MediaInfo };
+  get_cookies: { params: DomainParams; data: CookieInfo };
+  get_csrf_token: { params: JsonObject; data: CsrfInfo };
+  get_credentials: { params: DomainParams; data: CredentialsInfo };
+  set_restart: { params: JsonObject; data: EmptyData };
+  clean_cache: { params: JsonObject; data: EmptyData };
+  '.handle_quick_operation': { params: QuickOperationParams; data: EmptyData };
+  set_friend_remark: { params: SetFriendRemarkParams; data: EmptyData };
+  set_msg_emoji_like: { params: SetMsgEmojiLikeParams; data: EmptyData };
+  _mark_all_as_read: { params: JsonObject; data: EmptyData };
+  get_group_file_system_info: { params: GroupIdParams; data: GroupFileSystemInfo };
+  check_url_safely: { params: JsonObject; data: UrlSafetyInfo };
+  download_file: { params: DownloadFileParams; data: DownloadFileResult };
+  set_qq_profile: { params: SetQqProfileParams; data: EmptyData };
+  set_online_status: { params: SetOnlineStatusParams; data: EmptyData };
+  get_group_ignored_notifies: { params: JsonObject; data: JsonArray };
+  get_group_shut_list: { params: JsonObject; data: JsonArray };
+  forward_friend_single_msg: { params: JsonObject; data: JsonValue };
+  forward_group_single_msg: { params: JsonObject; data: JsonValue };
+  get_recent_contact: { params: JsonObject; data: JsonArray };
+  get_profile_like: { params: JsonObject; data: JsonObject };
+  get_friends_with_category: { params: JsonObject; data: JsonObject[] };
+  get_online_clients: { params: JsonObject; data: OnlineClientsInfo };
+  _get_model_show: { params: JsonObject; data: { variants: JsonArray } };
+  _set_model_show: { params: JsonObject; data: EmptyData };
+  '.get_word_slices': { params: JsonObject; data: JsonValue };
+  get_group_at_all_remain: { params: JsonObject; data: GroupAtAllRemainInfo };
+  get_unidirectional_friend_list: { params: JsonObject; data: JsonArray };
+  set_self_longnick: { params: JsonObject; data: EmptyData };
+  get_collection_list: { params: JsonObject; data: JsonArray };
+  create_collection: { params: JsonObject; data: JsonValue };
+  set_qq_avatar: { params: JsonObject; data: EmptyData };
+  set_input_status: { params: JsonObject; data: EmptyData };
+  translate_en2zh: { params: JsonObject; data: JsonValue };
+  get_clientkey: { params: JsonObject; data: ClientKeyInfo };
+  get_mini_app_ark: { params: JsonObject; data: JsonValue };
+  click_inline_keyboard_button: { params: JsonObject; data: JsonValue };
+  set_group_sign: { params: JsonObject; data: EmptyData };
+  send_group_sign: { params: JsonObject; data: EmptyData };
+  get_group_info_ex: { params: GroupIdParams; data: JsonObject };
+  get_group_detail_info: { params: GroupIdParams; data: JsonObject };
+  trans_group_file: { params: JsonObject; data: JsonValue };
+  rename_group_file: { params: JsonObject; data: JsonValue };
+  get_file: { params: GetMediaParams; data: JsonValue };
+  '.send_packet': { params: JsonObject; data: JsonValue };
+}
+
+export type SnowLumaAction = keyof SnowLumaActionMap | (string & {});
+
+export type ActionParams<TAction extends string> =
+  TAction extends keyof SnowLumaActionMap ? SnowLumaActionMap[TAction]['params'] : JsonObject;
+
+export type ActionResult<TAction extends string> =
+  TAction extends keyof SnowLumaActionMap ? SnowLumaActionMap[TAction]['data'] : ActionData;
diff --git a/packages/sdk/src/types/events.ts b/packages/sdk/src/types/events.ts
new file mode 100644
index 00000000..bb8e1eb3
--- /dev/null
+++ b/packages/sdk/src/types/events.ts
@@ -0,0 +1,73 @@
+import type { JsonObject, JsonValue } from './json';
+
+export interface OneBotBaseEvent extends JsonObject {
+  time: number;
+  self_id: number;
+  post_type: string;
+}
+
+export interface OneBotSender extends JsonObject {
+  user_id: number;
+  nickname: string;
+  sex?: string;
+  age?: number;
+  card?: string;
+  role?: string;
+}
+
+export interface OneBotPrivateMessageEvent extends OneBotBaseEvent {
+  post_type: 'message' | 'message_sent';
+  message_type: 'private';
+  sub_type: string;
+  message_id: number;
+  message_seq?: number;
+  user_id: number;
+  message: JsonValue;
+  raw_message: string;
+  font: number;
+  sender: OneBotSender;
+}
+
+export interface OneBotGroupMessageEvent extends OneBotBaseEvent {
+  post_type: 'message' | 'message_sent';
+  message_type: 'group';
+  sub_type: string;
+  message_id: number;
+  message_seq?: number;
+  group_id: number;
+  user_id: number;
+  message: JsonValue;
+  raw_message: string;
+  font: number;
+  sender: OneBotSender;
+  anonymous?: JsonValue;
+}
+
+export type OneBotMessageEvent = OneBotPrivateMessageEvent | OneBotGroupMessageEvent;
+
+export interface OneBotNoticeEvent extends OneBotBaseEvent {
+  post_type: 'notice';
+  notice_type: string;
+}
+
+export interface OneBotRequestEvent extends OneBotBaseEvent {
+  post_type: 'request';
+  request_type: string;
+  flag: string;
+  sub_type?: string;
+  group_id?: number;
+  user_id?: number;
+  comment?: string;
+}
+
+export interface OneBotMetaEvent extends OneBotBaseEvent {
+  post_type: 'meta_event';
+  meta_event_type: string;
+}
+
+export type SnowLumaEvent =
+  | OneBotMessageEvent
+  | OneBotNoticeEvent
+  | OneBotRequestEvent
+  | OneBotMetaEvent
+  | OneBotBaseEvent;
diff --git a/packages/sdk/src/types/index.ts b/packages/sdk/src/types/index.ts
new file mode 100644
index 00000000..2fd63d12
--- /dev/null
+++ b/packages/sdk/src/types/index.ts
@@ -0,0 +1,6 @@
+export * from './json';
+export * from './messages';
+export * from './results';
+export * from './params';
+export * from './actions';
+export * from './events';
diff --git a/packages/sdk/src/types/json.ts b/packages/sdk/src/types/json.ts
new file mode 100644
index 00000000..c30347f1
--- /dev/null
+++ b/packages/sdk/src/types/json.ts
@@ -0,0 +1,43 @@
+export type JsonPrimitive = string | number | boolean | null;
+export type JsonValue = JsonPrimitive | JsonObject | JsonArray;
+
+export interface JsonObject {
+  [key: string]: JsonValue | undefined;
+}
+
+export type JsonArray = JsonValue[];
+
+export interface ApiResponse<TData = JsonValue> {
+  status: 'ok' | 'failed';
+  retcode: number;
+  data: TData;
+  echo?: JsonValue;
+  wording?: string;
+}
+
+export interface OneBotRequest<TParams extends JsonObject = JsonObject> {
+  action: string;
+  params?: TParams;
+  echo?: JsonValue;
+}
+
+export type WsRole = 'Api' | 'Event' | 'Universal';
+export type MessageFormat = 'array' | 'string';
+
+/** Per-request controls shared by HTTP and WebSocket clients. */
+export interface RequestOptions {
+  /** Echo value used to correlate OneBot request and response packets. */
+  echo?: JsonValue;
+  /** Override the client's default timeout for this request. Set to 0 to disable timeout. */
+  timeoutMs?: number;
+  /** Cancels the request before a SnowLuma response arrives. */
+  signal?: AbortSignal;
+}
+
+/** Shared options accepted by concrete SnowLuma clients. */
+export interface SnowLumaClientOptions {
+  /** Access token configured in SnowLuma's OneBot settings. */
+  accessToken?: string;
+  /** Default timeout for API calls in milliseconds. Defaults to 30000. */
+  requestTimeoutMs?: number;
+}
diff --git a/packages/sdk/src/types/messages.ts b/packages/sdk/src/types/messages.ts
new file mode 100644
index 00000000..9ef837b9
--- /dev/null
+++ b/packages/sdk/src/types/messages.ts
@@ -0,0 +1,85 @@
+import type { JsonObject } from './json';
+
+export interface MessageSegment<
+  TType extends string = string,
+  TData extends Record<string, unknown> = JsonObject,
+> {
+  type: TType;
+  data: TData;
+}
+
+export type TextSegment = MessageSegment<'text', { text: string }>;
+export type FaceSegment = MessageSegment<'face', { id: string }>;
+export type AtSegment = MessageSegment<'at', { qq: string; name?: string; uid?: string }>;
+export type ReplySegment = MessageSegment<'reply', { id: string }>;
+export type ImageSegment = MessageSegment<'image', {
+  file: string;
+  type?: 'flash';
+  subType?: number;
+  summary?: string;
+  url?: string;
+}>;
+export type RecordSegment = MessageSegment<'record', { file: string; url?: string }>;
+export type VideoSegment = MessageSegment<'video', { file: string; url?: string; thumb?: string }>;
+export type JsonSegment = MessageSegment<'json', { data: string }>;
+export type XmlSegment = MessageSegment<'xml', { data: string; id?: string }>;
+export type PokeSegment = MessageSegment<'poke', { type: string | number; id?: string | number }>;
+export type ForwardSegment = MessageSegment<'forward', { id: string; res_id?: string; forward_id?: string }>;
+export type NodeSegment = MessageSegment<'node', {
+  user_id: number;
+  nickname: string;
+  content: OutgoingMessage;
+}>;
+export type ShareSegment = MessageSegment<'share', {
+  url: string;
+  title: string;
+  content?: string;
+  image?: string;
+}>;
+export type MusicSegment = MessageSegment<'music', {
+  type: string;
+  id?: string;
+  url?: string;
+  audio?: string;
+  title?: string;
+  image?: string;
+  content?: string;
+}>;
+export type LocationSegment = MessageSegment<'location', {
+  lat: string | number;
+  lon: string | number;
+  title?: string;
+  content?: string;
+}>;
+export type ContactSegment = MessageSegment<'contact', {
+  type: 'qq' | 'group' | string;
+  id: string | number;
+}>;
+
+export type KnownMessageSegment =
+  | TextSegment
+  | FaceSegment
+  | AtSegment
+  | ReplySegment
+  | ImageSegment
+  | RecordSegment
+  | VideoSegment
+  | JsonSegment
+  | XmlSegment
+  | PokeSegment
+  | ForwardSegment
+  | NodeSegment
+  | ShareSegment
+  | MusicSegment
+  | LocationSegment
+  | ContactSegment;
+
+export type AnyMessageSegment = KnownMessageSegment | MessageSegment;
+
+export interface MessageChainLike {
+  readonly length: number;
+  toSegments(): AnyMessageSegment[];
+  toJSON(): AnyMessageSegment[];
+}
+
+export type OutgoingMessage = string | MessageChainLike | AnyMessageSegment | AnyMessageSegment[];
diff --git a/packages/sdk/src/types/params.ts b/packages/sdk/src/types/params.ts
new file mode 100644
index 00000000..6f917ad2
--- /dev/null
+++ b/packages/sdk/src/types/params.ts
@@ -0,0 +1,279 @@
+import type { JsonObject, JsonValue } from './json';
+
+export interface SendMsgParams extends JsonObject {
+  message_type?: 'private' | 'group' | string;
+  user_id?: number;
+  group_id?: number;
+  message: JsonValue;
+  auto_escape?: boolean;
+}
+
+export interface SendPrivateMsgParams extends JsonObject {
+  user_id: number;
+  message: JsonValue;
+  auto_escape?: boolean;
+}
+
+export interface SendGroupMsgParams extends JsonObject {
+  group_id: number;
+  message: JsonValue;
+  auto_escape?: boolean;
+}
+
+export interface MessageIdParams extends JsonObject {
+  message_id: number;
+}
+
+export interface GroupIdParams extends JsonObject {
+  group_id: number;
+}
+
+export interface UserIdParams extends JsonObject {
+  user_id: number;
+}
+
+export interface NoCacheParams extends JsonObject {
+  no_cache?: boolean;
+}
+
+export interface GetGroupListParams extends NoCacheParams {}
+
+export interface GetGroupInfoParams extends GroupIdParams {
+  no_cache?: boolean;
+}
+
+export interface GetGroupMemberListParams extends GroupIdParams {
+  no_cache?: boolean;
+}
+
+export interface GetGroupMemberInfoParams extends GroupIdParams {
+  user_id: number;
+  no_cache?: boolean;
+}
+
+export interface GetGroupHonorInfoParams extends GroupIdParams {
+  type?: 'talkative' | 'performer' | 'legend' | 'strong_newbie' | 'emotion' | 'all' | string;
+}
+
+export interface DeleteFriendParams extends UserIdParams {
+  block?: boolean;
+}
+
+export interface SetGroupKickParams extends GroupIdParams {
+  user_id: number;
+  reject_add_request?: boolean;
+}
+
+export interface SetGroupBanParams extends GroupIdParams {
+  user_id: number;
+  duration?: number;
+}
+
+export interface SetGroupWholeBanParams extends GroupIdParams {
+  enable?: boolean;
+}
+
+export interface SetGroupAdminParams extends GroupIdParams {
+  user_id: number;
+  enable?: boolean;
+}
+
+export interface SetGroupCardParams extends GroupIdParams {
+  user_id: number;
+  card?: string;
+}
+
+export interface SetGroupNameParams extends GroupIdParams {
+  group_name: string;
+}
+
+export interface SetGroupSpecialTitleParams extends GroupIdParams {
+  user_id: number;
+  special_title?: string;
+}
+
+export interface UploadGroupFileParams extends GroupIdParams {
+  file: string;
+  name?: string;
+  folder?: string;
+  folder_id?: string;
+  upload_file?: boolean;
+}
+
+export interface UploadPrivateFileParams extends UserIdParams {
+  file: string;
+  name?: string;
+  upload_file?: boolean;
+}
+
+export interface GetGroupFileUrlParams extends GroupIdParams {
+  file_id: string;
+  busid?: number;
+}
+
+export interface GetGroupFilesParams extends GroupIdParams {
+  folder_id?: string;
+  folder?: string;
+}
+
+export interface DeleteGroupFileParams extends GroupIdParams {
+  file_id: string;
+}
+
+export interface MoveGroupFileParams extends GroupIdParams {
+  file_id: string;
+  parent_directory: string;
+  target_directory: string;
+}
+
+export interface CreateGroupFileFolderParams extends GroupIdParams {
+  name: string;
+  parent_id?: string;
+}
+
+export interface DeleteGroupFileFolderParams extends GroupIdParams {
+  folder_id: string;
+}
+
+export interface RenameGroupFileFolderParams extends GroupIdParams {
+  folder_id: string;
+  new_folder_name?: string;
+  name?: string;
+}
+
+export interface GetPrivateFileUrlParams extends UserIdParams {
+  file_id: string;
+  file_hash: string;
+}
+
+export interface SetFriendAddRequestParams extends JsonObject {
+  flag: string;
+  approve?: boolean;
+}
+
+export interface SetGroupAddRequestParams extends JsonObject {
+  flag: string;
+  sub_type?: string;
+  type?: string;
+  approve?: boolean;
+  reason?: string;
+}
+
+export interface SendLikeParams extends UserIdParams {
+  times?: number;
+}
+
+export interface FriendPokeParams extends UserIdParams {
+  target_id?: number;
+}
+
+export interface GroupPokeParams extends GroupIdParams {
+  user_id: number;
+}
+
+export interface SendPokeParams extends UserIdParams {
+  group_id?: number;
+}
+
+export interface SetGroupReactionParams extends JsonObject {
+  message_id: number;
+  code: string;
+  group_id?: number;
+  is_set?: boolean;
+}
+
+export interface GetMessageHistoryParams extends JsonObject {
+  message_id?: number;
+  count?: number;
+}
+
+export interface GetGroupMessageHistoryParams extends GroupIdParams, GetMessageHistoryParams {}
+export interface GetFriendMessageHistoryParams extends UserIdParams, GetMessageHistoryParams {}
+
+export interface MarkGroupMsgAsReadParams extends JsonObject {
+  message_id: number;
+  group_id?: number;
+}
+
+export interface MarkPrivateMsgAsReadParams extends JsonObject {
+  message_id: number;
+  user_id?: number;
+}
+
+export interface MarkMsgAsReadParams extends JsonObject {
+  message_id: number;
+  target_id?: number;
+}
+
+export interface GroupNoticeParams extends GroupIdParams {
+  content: string;
+  image?: string;
+  pinned?: number;
+  type?: number;
+  confirm_required?: number;
+}
+
+export interface ForwardMessageParams extends JsonObject {
+  message_type?: 'private' | 'group' | string;
+  user_id?: number;
+  group_id?: number;
+  message?: JsonValue;
+  messages?: JsonValue;
+}
+
+export interface GroupForwardMessageParams extends GroupIdParams {
+  message?: JsonValue;
+  messages?: JsonValue;
+}
+
+export interface PrivateForwardMessageParams extends UserIdParams {
+  message?: JsonValue;
+  messages?: JsonValue;
+}
+
+export interface GetForwardMsgParams extends JsonObject {
+  id?: string;
+  message_id?: number | string;
+}
+
+export interface GetMediaParams extends JsonObject {
+  file?: string;
+  file_id?: string;
+}
+
+export interface DomainParams extends JsonObject {
+  domain?: string;
+}
+
+export interface QuickOperationParams extends JsonObject {
+  context: JsonObject;
+  operation: JsonObject;
+}
+
+export interface SetFriendRemarkParams extends UserIdParams {
+  remark: string;
+}
+
+export interface SetMsgEmojiLikeParams extends JsonObject {
+  message_id: number;
+  emoji_id: string;
+  set?: boolean;
+}
+
+export interface DownloadFileParams extends JsonObject {
+  url?: string;
+  base64?: string;
+  name?: string;
+  headers?: string | string[];
+}
+
+export interface SetQqProfileParams extends JsonObject {
+  nickname?: string;
+  personal_note?: string;
+}
+
+export interface SetOnlineStatusParams extends JsonObject {
+  status: number;
+  ext_status?: number;
+  battery_status?: number;
+}
diff --git a/packages/sdk/src/types/results.ts b/packages/sdk/src/types/results.ts
new file mode 100644
index 00000000..37cd1e35
--- /dev/null
+++ b/packages/sdk/src/types/results.ts
@@ -0,0 +1,103 @@
+import type { JsonArray, JsonObject } from './json';
+
+export interface SendMessageResult {
+  message_id: number;
+}
+
+export interface ForwardMessageResult {
+  message_id: number;
+  res_id: string;
+  forward_id: string;
+}
+
+export interface UploadForwardResult {
+  message_id: number;
+  res_id: string;
+  forward_id: string;
+  group_id?: number;
+}
+
+export interface LoginInfo {
+  user_id: number;
+  nickname: string;
+}
+
+export interface StatusInfo {
+  online: boolean;
+  good: boolean;
+}
+
+export interface VersionInfo {
+  app_name: string;
+  app_version: string;
+  protocol_version: string;
+}
+
+export interface CapabilityInfo {
+  yes: boolean;
+}
+
+export interface GroupFileUrl {
+  url: string;
+}
+
+export interface PrivateFileUrl {
+  url: string;
+}
+
+export interface GroupFileSystemInfo {
+  file_count: number;
+  limit_count: number;
+  used_space: number;
+  total_space: number;
+}
+
+export interface GroupMessageHistory {
+  messages: JsonObject[];
+}
+
+export interface FriendMessageHistory {
+  messages: JsonObject[];
+}
+
+export interface MediaInfo extends JsonObject {}
+
+export interface CookieInfo {
+  cookies: string;
+}
+
+export interface CsrfInfo {
+  token: number;
+}
+
+export interface CredentialsInfo {
+  cookies: string;
+  token: number;
+  csrf_token: number;
+}
+
+export interface DownloadFileResult {
+  file: string;
+}
+
+export interface ClientKeyInfo {
+  clientKey: string;
+  keyIndex: string;
+  expireTime: string;
+}
+
+export interface OnlineClientsInfo {
+  clients: JsonArray;
+}
+
+export interface UrlSafetyInfo {
+  level: number;
+}
+
+export interface GroupAtAllRemainInfo {
+  can_at_all: boolean;
+  remain_at_all_count_for_group: number;
+  remain_at_all_count_for_uin: number;
+}
+
+export type EmptyData = null;
diff --git a/packages/sdk/tests/actions-sync.test.ts b/packages/sdk/tests/actions-sync.test.ts
new file mode 100644
index 00000000..5b31386e
--- /dev/null
+++ b/packages/sdk/tests/actions-sync.test.ts
@@ -0,0 +1,21 @@
+import fs from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { describe, expect, it } from 'vitest';
+import { SNOWLUMA_ACTIONS } from '../src';
+
+describe('SnowLuma action list', () => {
+  it('stays in sync with core registerAction calls', () => {
+    const actionsDir = fileURLToPath(new URL('../../core/src/onebot/actions/', import.meta.url));
+    const registered = new Set<string>();
+
+    for (const file of fs.readdirSync(actionsDir)) {
+      if (!file.endsWith('.ts')) continue;
+      const source = fs.readFileSync(new URL(file, `file://${actionsDir}/`), 'utf8');
+      for (const match of source.matchAll(/registerAction\('([^']+)'/g)) {
+        registered.add(match[1]!);
+      }
+    }
+
+    expect([...SNOWLUMA_ACTIONS].sort()).toEqual([...registered].sort());
+  });
+});
diff --git a/packages/sdk/tests/events.test.ts b/packages/sdk/tests/events.test.ts
new file mode 100644
index 00000000..25b70378
--- /dev/null
+++ b/packages/sdk/tests/events.test.ts
@@ -0,0 +1,88 @@
+import { describe, expect, it, vi } from 'vitest';
+import {
+  createEventContext,
+  isGroupMessageEvent,
+  isPrivateMessageEvent,
+  matchCommand,
+  text,
+  type OneBotPrivateMessageEvent,
+  type OneBotRequestEvent,
+  type SnowLumaApiClient,
+} from '../src';
+
+const PRIVATE_EVENT: OneBotPrivateMessageEvent = {
+  time: 1,
+  self_id: 10000,
+  post_type: 'message',
+  message_type: 'private',
+  sub_type: 'friend',
+  message_id: 7,
+  message_seq: 8,
+  user_id: 10001,
+  message: [{ type: 'text', data: { text: '/ping a b' } }],
+  raw_message: '/ping a b',
+  font: 0,
+  sender: { user_id: 10001, nickname: 'tester' },
+};
+
+function fakeClient(): SnowLumaApiClient {
+  return {
+    sendPrivateMessage: vi.fn().mockResolvedValue({ message_id: 1 }),
+    sendGroupMessage: vi.fn().mockResolvedValue({ message_id: 2 }),
+    setFriendAddRequest: vi.fn().mockResolvedValue(null),
+    setGroupAddRequest: vi.fn().mockResolvedValue(null),
+    raw: vi.fn().mockResolvedValue(null),
+  } as unknown as SnowLumaApiClient;
+}
+
+describe('event helpers', () => {
+  it('narrows message event types', () => {
+    expect(isPrivateMessageEvent(PRIVATE_EVENT)).toBe(true);
+    expect(isGroupMessageEvent(PRIVATE_EVENT)).toBe(false);
+  });
+
+  it('replies to private messages through context', async () => {
+    const client = fakeClient();
+    const context = createEventContext(PRIVATE_EVENT, client);
+
+    await context.reply(text('pong'));
+
+    expect(client.sendPrivateMessage).toHaveBeenCalledWith(10001, text('pong'), undefined);
+  });
+
+  it('approves and rejects request events', async () => {
+    const client = fakeClient();
+    const request: OneBotRequestEvent = {
+      time: 1,
+      self_id: 10000,
+      post_type: 'request',
+      request_type: 'group',
+      sub_type: 'invite',
+      flag: 'flag-1',
+    };
+    const context = createEventContext(request, client);
+
+    await context.approve();
+    await context.reject('nope');
+
+    expect(client.setGroupAddRequest).toHaveBeenNthCalledWith(1, 'flag-1', {
+      subType: 'invite',
+      approve: true,
+    });
+    expect(client.setGroupAddRequest).toHaveBeenNthCalledWith(2, 'flag-1', {
+      subType: 'invite',
+      approve: false,
+      reason: 'nope',
+    });
+  });
+
+  it('matches commands with prefixes', () => {
+    expect(matchCommand(PRIVATE_EVENT, 'ping')).toMatchObject({
+      command: 'ping',
+      args: ['a', 'b'],
+      rest: 'a b',
+      prefix: '/',
+    });
+    expect(matchCommand(PRIVATE_EVENT, 'pong')).toBeNull();
+  });
+});
diff --git a/packages/sdk/tests/http-client.test.ts b/packages/sdk/tests/http-client.test.ts
new file mode 100644
index 00000000..b4f8215b
--- /dev/null
+++ b/packages/sdk/tests/http-client.test.ts
@@ -0,0 +1,44 @@
+import { describe, expect, it, vi } from 'vitest';
+import {
+  SnowLumaAbortError,
+  SnowLumaAuthError,
+  SnowLumaHttpClient,
+  SnowLumaParseError,
+} from '../src';
+
+describe('SnowLumaHttpClient', () => {
+  it('throws SnowLumaAuthError for auth retcodes', async () => {
+    const fetchImpl = vi.fn().mockResolvedValue(new Response(JSON.stringify({
+      status: 'failed',
+      retcode: 1401,
+      data: null,
+      wording: 'unauthorized',
+    })));
+    const client = new SnowLumaHttpClient({ fetch: fetchImpl });
+
+    await expect(client.getStatus()).rejects.toBeInstanceOf(SnowLumaAuthError);
+  });
+
+  it('throws SnowLumaParseError for non-JSON responses', async () => {
+    const fetchImpl = vi.fn().mockResolvedValue(new Response('not json', { status: 200 }));
+    const client = new SnowLumaHttpClient({ fetch: fetchImpl });
+
+    await expect(client.getStatus()).rejects.toBeInstanceOf(SnowLumaParseError);
+  });
+
+  it('supports caller AbortSignal cancellation', async () => {
+    const fetchImpl = vi.fn((_url: string | URL | Request, init?: RequestInit) => new Promise<Response>((_resolve, reject) => {
+      const signal = init?.signal;
+      const abort = () => reject(new DOMException('aborted', 'AbortError'));
+      if (signal?.aborted) abort();
+      signal?.addEventListener('abort', abort, { once: true });
+    }));
+    const client = new SnowLumaHttpClient({ fetch: fetchImpl });
+    const controller = new AbortController();
+
+    const request = client.getStatus({ signal: controller.signal });
+    controller.abort();
+
+    await expect(request).rejects.toBeInstanceOf(SnowLumaAbortError);
+  });
+});
diff --git a/packages/sdk/tests/messages.test.ts b/packages/sdk/tests/messages.test.ts
new file mode 100644
index 00000000..0749e4cb
--- /dev/null
+++ b/packages/sdk/tests/messages.test.ts
@@ -0,0 +1,62 @@
+import { describe, expect, it, vi } from 'vitest';
+import {
+  atAll,
+  fromCQString,
+  message,
+  parseSegments,
+  text,
+  toCQString,
+} from '../src';
+
+describe('MessageChain', () => {
+  it('builds fluent segment chains', () => {
+    const chain = text('hello').at(10001).br().image('/tmp/a.png');
+
+    expect(chain.length).toBe(4);
+    expect(chain.toSegments()).toEqual([
+      { type: 'text', data: { text: 'hello' } },
+      { type: 'at', data: { qq: '10001' } },
+      { type: 'text', data: { text: '\n' } },
+      { type: 'image', data: { file: '/tmp/a.png' } },
+    ]);
+  });
+
+  it('keeps the old segment builder API available', () => {
+    expect(message.text('hello')).toEqual({ type: 'text', data: { text: 'hello' } });
+    expect(atAll().toSegments()).toEqual([{ type: 'at', data: { qq: 'all' } }]);
+  });
+
+  it('allows reply only once in a chain at runtime', () => {
+    const chain = text('hello').reply(1);
+    expect(() => (chain as any).reply(2)).toThrow(/reply/);
+    expect(() => chain.append(message.reply(2))).toThrow(/reply/);
+  });
+
+  it('appends other messages and converts to CQ string', () => {
+    const chain = text('hello').append([message.at('all'), message.face(14)]);
+    expect(toCQString(chain)).toBe('hello[CQ:at,qq=all][CQ:face,id=14]');
+  });
+
+  it('parses CQ strings into chains', () => {
+    const chain = fromCQString('hi[CQ:at,qq=all][CQ:image,file=a&#44;b]');
+    expect(chain.toSegments()).toEqual([
+      { type: 'text', data: { text: 'hi' } },
+      { type: 'at', data: { qq: 'all' } },
+      { type: 'image', data: { file: 'a,b', url: undefined, type: undefined, summary: undefined } },
+    ]);
+    expect(parseSegments('[CQ:reply,id=7]')).toEqual([{ type: 'reply', data: { id: '7' } }]);
+  });
+
+  it('can send itself through a compatible client', async () => {
+    const client = {
+      sendGroupMessage: vi.fn().mockResolvedValue({ message_id: 1 }),
+      sendPrivateMessage: vi.fn().mockResolvedValue({ message_id: 2 }),
+    };
+
+    await text('hi').sendToGroup(client, 123);
+    await text('yo').sendToPrivate(client, 456);
+
+    expect(client.sendGroupMessage).toHaveBeenCalledWith(123, text('hi'), undefined);
+    expect(client.sendPrivateMessage).toHaveBeenCalledWith(456, text('yo'), undefined);
+  });
+});
diff --git a/packages/sdk/tests/websocket-client.test.ts b/packages/sdk/tests/websocket-client.test.ts
new file mode 100644
index 00000000..2258dfb6
--- /dev/null
+++ b/packages/sdk/tests/websocket-client.test.ts
@@ -0,0 +1,143 @@
+import { describe, expect, it, vi } from 'vitest';
+import {
+  SnowLumaAbortError,
+  SnowLumaWebSocketClient,
+  type OneBotPrivateMessageEvent,
+} from '../src';
+
+class MockWebSocket {
+  static instances: MockWebSocket[] = [];
+
+  readyState = 0;
+  sent: string[] = [];
+  readonly listeners = new Map<string, Set<(...args: unknown[]) => void>>();
+
+  constructor(
+    readonly url: string,
+    readonly protocols?: string | string[],
+  ) {
+    MockWebSocket.instances.push(this);
+  }
+
+  addEventListener(event: string, listener: (...args: unknown[]) => void): void {
+    let listeners = this.listeners.get(event);
+    if (!listeners) {
+      listeners = new Set();
+      this.listeners.set(event, listeners);
+    }
+    listeners.add(listener);
+  }
+
+  removeEventListener(event: string, listener: (...args: unknown[]) => void): void {
+    this.listeners.get(event)?.delete(listener);
+  }
+
+  send(data: string): void {
+    this.sent.push(data);
+  }
+
+  close(code?: number, reason?: string): void {
+    this.readyState = 3;
+    this.emit('close', { code, reason });
+  }
+
+  open(): void {
+    this.readyState = 1;
+    this.emit('open');
+  }
+
+  message(data: unknown): void {
+    this.emit('message', { data });
+  }
+
+  emit(event: string, ...args: unknown[]): void {
+    for (const listener of this.listeners.get(event) ?? []) {
+      listener(...args);
+    }
+  }
+}
+
+const PRIVATE_EVENT: OneBotPrivateMessageEvent = {
+  time: 1,
+  self_id: 10000,
+  post_type: 'message',
+  message_type: 'private',
+  sub_type: 'friend',
+  message_id: 7,
+  message_seq: 8,
+  user_id: 10001,
+  message: [{ type: 'text', data: { text: '/ping a b' } }],
+  raw_message: '/ping a b',
+  font: 0,
+  sender: { user_id: 10001, nickname: 'tester' },
+};
+
+describe('SnowLumaWebSocketClient', () => {
+  it('matches API responses by echo', async () => {
+    MockWebSocket.instances = [];
+    const client = new SnowLumaWebSocketClient({
+      url: 'ws://127.0.0.1:3001/',
+      accessToken: 'token',
+      webSocket: MockWebSocket,
+    });
+
+    const connecting = client.connect();
+    const socket = MockWebSocket.instances[0]!;
+    expect(socket.url).toContain('access_token=token');
+    socket.open();
+    await connecting;
+
+    const status = client.getStatus();
+    await vi.waitFor(() => expect(socket.sent).toHaveLength(1));
+    const request = JSON.parse(socket.sent[0]!) as { echo: string };
+    socket.message(JSON.stringify({
+      status: 'ok',
+      retcode: 0,
+      data: { online: true, good: true },
+      echo: request.echo,
+    }));
+
+    await expect(status).resolves.toEqual({ online: true, good: true });
+  });
+
+  it('runs command handlers for matching message events', async () => {
+    MockWebSocket.instances = [];
+    const client = new SnowLumaWebSocketClient({
+      url: 'ws://127.0.0.1:3001/',
+      webSocket: MockWebSocket,
+    });
+    const handler = vi.fn();
+    client.command('ping', handler);
+
+    const connecting = client.connect();
+    const socket = MockWebSocket.instances[0]!;
+    socket.open();
+    await connecting;
+    socket.message(JSON.stringify(PRIVATE_EVENT));
+
+    await vi.waitFor(() => {
+      expect(handler).toHaveBeenCalledTimes(1);
+      expect(handler.mock.calls[0]![2]).toMatchObject({ args: ['a', 'b'] });
+    });
+  });
+
+  it('supports caller AbortSignal cancellation for pending requests', async () => {
+    MockWebSocket.instances = [];
+    const client = new SnowLumaWebSocketClient({
+      url: 'ws://127.0.0.1:3001/',
+      webSocket: MockWebSocket,
+    });
+    const controller = new AbortController();
+
+    const connecting = client.connect();
+    const socket = MockWebSocket.instances[0]!;
+    socket.open();
+    await connecting;
+
+    const request = client.getStatus({ signal: controller.signal });
+    await vi.waitFor(() => expect(socket.sent).toHaveLength(1));
+    controller.abort();
+
+    await expect(request).rejects.toBeInstanceOf(SnowLumaAbortError);
+  });
+});
diff --git a/packages/sdk/tsconfig.json b/packages/sdk/tsconfig.json
new file mode 100644
index 00000000..17639fc0
--- /dev/null
+++ b/packages/sdk/tsconfig.json
@@ -0,0 +1,13 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "./dist",
+    "rootDir": "./src",
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true,
+    "lib": ["ES2022", "DOM"]
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist"]
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index daf6cd1e..e427a699 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -66,6 +66,18 @@ importers:
 
   packages/runtime: {}
 
+  packages/sdk:
+    devDependencies:
+      '@types/node':
+        specifier: ^24.12.2
+        version: 24.12.2
+      typescript:
+        specifier: 'catalog:'
+        version: 6.0.2
+      vitest:
+        specifier: ^4.1.4
+        version: 4.1.4(@types/node@24.12.2)(vite@8.0.8(@types/node@24.12.2)(esbuild@0.27.7)(jiti@2.6.1)(sass@1.99.0)(tsx@4.21.0))
+
   packages/websocket:
     devDependencies:
       '@types/node':
diff --git a/tsconfig.json b/tsconfig.json
index 4f1bc219..392df672 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -5,6 +5,7 @@
   "include": [],
   "references": [
     { "path": "./packages/core" },
+    { "path": "./packages/sdk" },
     { "path": "./packages/webui" }
   ]
 }