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Documentation Index

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The Claude Code SDK lets you drive Claude Code programmatically from TypeScript or JavaScript. You can send prompts, stream responses, manage multi-turn sessions, and build tools that run in the same process.

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Installation

npm install @anthropic-ai/claude-code

yarn add @anthropic-ai/claude-code

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The query() function

query() is the core primitive. It accepts a prompt string (or an async iterable of user messages) and returns an async iterable of SDKMessage objects. 
import { query } from '@anthropic-ai/claude-code'

const stream = query({
  prompt: 'List the files in the current directory',
  options: {
    maxTurns: 5,
  },
})

for await (const message of stream) {
  if (message.type === 'assistant') {
    console.log(message.message.content)
  }
  if (message.type === 'result') {
    console.log('Session cost:', message.usage?.costUSD)
  }
}

​
Streaming user messages

Pass an AsyncIterable<SDKUserMessage> as the prompt to send follow-up messages mid-stream: 
import { query } from '@anthropic-ai/claude-code'
import type { SDKUserMessage } from '@anthropic-ai/claude-code'

async function* userMessages(): AsyncIterable<SDKUserMessage> {
  yield { type: 'user', message: { role: 'user', content: 'Hello!' } }
  await someDelay()
  yield { type: 'user', message: { role: 'user', content: 'Now run the tests.' } }
}

for await (const message of query({ prompt: userMessages() })) {
  // handle messages
}

​
Key types

Messages yielded by query() are a discriminated union keyed on type:
typeDescription
userA user turn (echoed back)
assistantAn assistant turn with content blocks
tool_useClaude invoking a tool
tool_resultThe result of a tool call
resultFinal result message with usage stats
systemSystem-level metadata
for await (const msg of query({ prompt: 'Summarize this repo' })) {
  switch (msg.type) {
    case 'assistant':
      // msg.message.content is ContentBlock[]
      break
    case 'result':
      // msg.subtype is 'success' | 'error_max_turns' | ...
      // msg.usage contains token counts and cost
      break
  }
}
Pass an Options object to control behavior:
const stream = query({
  prompt: 'Fix the type errors',
  options: {
    // Working directory
    cwd: '/path/to/project',

    // Max agent turns before stopping
    maxTurns: 10,

    // Model override
    model: 'claude-sonnet-4-6',

    // Custom system prompt
    systemPrompt: 'You are a TypeScript expert.',

    // Append to the default system prompt
    appendSystemPrompt: 'Always prefer const over let.',

    // Permission mode
    permissionMode: 'acceptEdits',

    // Allowed tools (restrict what Claude can use)
    allowedTools: ['Read', 'Bash', 'Edit'],

    // MCP server configurations
    mcpServers: {
      myServer: {
        type: 'stdio',
        command: 'node',
        args: ['./mcp-server.js'],
      },
    },
  },
})
The result message includes usage data:
if (msg.type === 'result') {
  const usage = msg.usage
  // {
  //   inputTokens: number
  //   outputTokens: number
  //   cacheReadInputTokens: number
  //   cacheCreationInputTokens: number
  //   webSearchRequests: number
  //   costUSD: number
  //   contextWindow: number
  //   maxOutputTokens: number
  // }
}

​
Session management (V2 API)

The V2 API provides persistent multi-turn sessions. These APIs are currently unstable (@alpha).
The V2 session APIs are prefixed with unstable_v2_. Signatures may change in future releases.

​
Creating a session

import { unstable_v2_createSession } from '@anthropic-ai/claude-code'

const session = unstable_v2_createSession({
  model: 'claude-sonnet-4-6',
  cwd: '/path/to/project',
  permissionMode: 'acceptEdits',
})

​
Sending messages to a session

// Send a message and stream the response
for await (const message of session.query('What files are here?')) {
  console.log(message)
}

// Send a follow-up (same session context)
for await (const message of session.query('Now edit the README')) {
  console.log(message)
}

​
Resuming a session

import { unstable_v2_resumeSession } from '@anthropic-ai/claude-code'

const session = unstable_v2_resumeSession(sessionId, {
  model: 'claude-sonnet-4-6',
})

​
One-shot convenience function

For single prompts without managing a session object: 
import { unstable_v2_prompt } from '@anthropic-ai/claude-code'

const result = await unstable_v2_prompt('What files are here?', {
  model: 'claude-sonnet-4-6',
  cwd: '/path/to/project',
})
// result is an SDKResultMessage

​
Session utilities

These functions read and manage session transcripts stored on disk.

listSessions

List sessions with metadata, optionally filtered by project directory. Supports limit and offset for pagination.
const sessions = await listSessions({ dir: '/path/to/project' })
const page2 = await listSessions({ limit: 50, offset: 50 })

getSessionInfo

Read metadata for a single session by ID without scanning all sessions.
const info = await getSessionInfo(sessionId, { dir: '/path/to/project' })

getSessionMessages

Read conversation messages from a session’s JSONL transcript. Returns messages in chronological order.
const messages = await getSessionMessages(sessionId, {
  limit: 100,
  offset: 0,
  includeSystemMessages: false,
})

forkSession

Fork a session into a new branch with fresh UUIDs. Supports branching from a specific message with upToMessageId.
const { sessionId: newId } = await forkSession(sessionId, {
  upToMessageId: messageUuid,
  title: 'Experiment branch',
})

​
Renaming and tagging sessions

import { renameSession, tagSession } from '@anthropic-ai/claude-code'

// Rename
await renameSession(sessionId, 'My refactoring session')

// Tag
await tagSession(sessionId, 'needs-review')

// Clear a tag
await tagSession(sessionId, null)

​
Custom MCP tools

Register tools that run in the same process as the SDK: 
import { tool, createSdkMcpServer, query } from '@anthropic-ai/claude-code'
import { z } from 'zod'

const getWeather = tool(
  'get_weather',
  'Get the current weather for a city',
  {
    city: z.string().describe('The city name'),
  },
  async ({ city }) => ({
    content: [{ type: 'text', text: `Weather in ${city}: sunny, 22°C` }],
  }),
)

const server = createSdkMcpServer({
  name: 'my-tools',
  version: '1.0.0',
  tools: [getWeather],
})

for await (const msg of query({
  prompt: "What's the weather in London?",
  options: {
    mcpServers: {
      'my-tools': server,
    },
  },
})) {
  console.log(msg)
}
If your in-process MCP tool calls will run longer than 60 seconds, set the CLAUDE_CODE_STREAM_CLOSE_TIMEOUT environment variable to a higher value.

​
Error handling

import { query, AbortError } from '@anthropic-ai/claude-code'

const controller = new AbortController()

try {
  for await (const msg of query({
    prompt: 'Run the full test suite',
    options: { abortController: controller },
  })) {
    if (shouldCancel()) controller.abort()
    console.log(msg)
  }
} catch (err) {
  if (err instanceof AbortError) {
    console.log('Query was aborted')
  } else {
    throw err
  }
}

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