Claude Agent SDK for Python

Python SDK for Claude Agent. See the Claude Agent SDK documentation for more information.

Installation

pip install claude-agent-sdk

Prerequisites:

• Python 3.10+

Note: The Claude Code CLI is automatically bundled with the package - no separate installation required! The SDK will use the bundled CLI by default. If you prefer to use a system-wide installation or a specific version, you can:

• Install Claude Code separately: curl -fsSL https://claude.ai/install.sh | bash
• Specify a custom path: ClaudeAgentOptions(cli_path="/path/to/claude")

Quick Start

import anyio
from claude_agent_sdk import query

async def main():
    async for message in query(prompt="What is 2 + 2?"):
        print(message)

anyio.run(main)

Basic Usage: query()

query() is an async function for querying Claude Code. It returns an AsyncIterator of response messages. See src/claude_agent_sdk/query.py.

from claude_agent_sdk import query, ClaudeAgentOptions, AssistantMessage, TextBlock

# Simple query
async for message in query(prompt="Hello Claude"):
    if isinstance(message, AssistantMessage):
        for block in message.content:
            if isinstance(block, TextBlock):
                print(block.text)

# With options
options = ClaudeAgentOptions(
    system_prompt="You are a helpful assistant",
    max_turns=1
)

async for message in query(prompt="Tell me a joke", options=options):
    print(message)

Using Tools

By default, Claude has access to the full Claude Code toolset (Read, Write, Edit, Bash, and others). allowed_tools is a permission allowlist: listed tools are auto-approved, and unlisted tools fall through to permission_mode and can_use_tool for a decision. It does not remove tools from Claude's toolset. To block specific tools, use disallowed_tools. See the permissions guide for the full evaluation order.

options = ClaudeAgentOptions(
    allowed_tools=["Read", "Write", "Bash"],  # auto-approve these tools
    permission_mode='acceptEdits'  # auto-accept file edits
)

async for message in query(
    prompt="Create a hello.py file",
    options=options
):
    # Process tool use and results
    pass

Working Directory

from pathlib import Path

options = ClaudeAgentOptions(
    cwd="/path/to/project"  # or Path("/path/to/project")
)

System Prompt

By default, Claude Code builds the system prompt on a session's first request, records it, and reuses it on every later request, including after you resume the session. A changed custom prompt, or changed append text on the claude_code preset, then has no effect until the session is compacted or you start a new session. To rebuild the prompt on every request instead, for example while you iterate on its wording, set snapshot to False in the {"type": "preset", ...} or {"type": "custom", ...} dict:

options = ClaudeAgentOptions(
    system_prompt={"type": "custom", "prompt": "You are a release bot.", "snapshot": False}
)

Requires Claude Code CLI 2.1.257 or later. Before 2.1.265, a session with an append or custom prompt recorded it only when snapshot was True. See Modifying system prompts for details.

ClaudeSDKClient

ClaudeSDKClient supports bidirectional, interactive conversations with Claude Code. See src/claude_agent_sdk/client.py.

Unlike query(), ClaudeSDKClient additionally enables custom tools and hooks, both of which can be defined as Python functions.

Custom Tools (as In-Process SDK MCP Servers)

A custom tool is a Python function that you can offer to Claude, for Claude to invoke as needed.

Custom tools are implemented in-process MCP servers that run directly within your Python application, eliminating the need for separate processes that regular MCP servers require.

For an end-to-end example, see MCP Calculator.

Creating a Simple Tool

from claude_agent_sdk import tool, create_sdk_mcp_server, ClaudeAgentOptions, ClaudeSDKClient

# Define a tool using the @tool decorator
@tool("greet", "Greet a user", {"name": str})
async def greet_user(args):
    return {
        "content": [
            {"type": "text", "text": f"Hello, {args['name']}!"}
        ]
    }

# Create an SDK MCP server
server = create_sdk_mcp_server(
    name="my-tools",
    version="1.0.0",
    tools=[greet_user]
)

# Use it with Claude. allowed_tools pre-approves the tool so it runs
# without a permission prompt; it does not control tool availability.
options = ClaudeAgentOptions(
    mcp_servers={"tools": server},
    allowed_tools=["mcp__tools__greet"]
)

async with ClaudeSDKClient(options=options) as client:
    await client.query("Greet Alice")

    # Extract and print response
    async for msg in client.receive_response():
        print(msg)

Benefits Over External MCP Servers

• No subprocess management - Runs in the same process as your application
• Better performance - No IPC overhead for tool calls
• Simpler deployment - Single Python process instead of multiple
• Easier debugging - All code runs in the same process
• Type safety - Direct Python function calls with type hints

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