Documentation Index

Fetch the complete documentation index at: https://code.claude.com/docs/llms.txt Use this file to discover all available pages before exploring further.

Connect to external tools with MCP

Configure MCP servers to extend your agent with external tools. Covers transport types, tool search for large tool sets, authentication, and error handling.

The Model Context Protocol (MCP) is an open standard for connecting AI agents to external tools and data sources. With MCP, your agent can query databases, integrate with APIs like Slack and GitHub, and connect to other services without writing custom tool implementations.

MCP servers can run as local processes, connect over HTTP, or execute directly within your SDK application.

Quickstart

This example connects to the Claude Code documentation MCP server using HTTP transport and uses allowedTools with a wildcard to permit all tools from the server.

for await (const message of query({
  prompt: "Use the docs MCP server to explain what hooks are in Claude Code",
  options: {
    mcpServers: {
      "claude-code-docs": {
        type: "http",
        url: "https://code.claude.com/docs/mcp"
      }
    },
    allowedTools: ["mcp__claude-code-docs__*"]
  }
})) {
  if (message.type === "result" && message.subtype === "success") {
    console.log(message.result);
  }
}

from claude_agent_sdk import query, ClaudeAgentOptions, ResultMessage

async def main():
    options = ClaudeAgentOptions(
        mcp_servers={
            "claude-code-docs": {
                "type": "http",
                "url": "https://code.claude.com/docs/mcp",
            }
        },
        allowed_tools=["mcp__claude-code-docs__*"],
    )

    async for message in query(
        prompt="Use the docs MCP server to explain what hooks are in Claude Code",
        options=options,
    ):
        if isinstance(message, ResultMessage) and message.subtype == "success":
            print(message.result)

asyncio.run(main())

The agent connects to the documentation server, searches for information about hooks, and returns the results.

Add an MCP server

You can configure MCP servers in code when calling query(), or in a .mcp.json file loaded via settingSources.

In code

Pass MCP servers directly in the mcpServers option:

for await (const message of query({
  prompt: "List files in my project",
  options: {
    mcpServers: {
      filesystem: {
        command: "npx",
        args: ["-y", "@modelcontextprotocol/server-filesystem", "/Users/me/projects"]
      }
    },
    allowedTools: ["mcp__filesystem__*"]
  }
})) {
  if (message.type === "result" && message.subtype === "success") {
    console.log(message.result);
  }
}

from claude_agent_sdk import query, ClaudeAgentOptions, ResultMessage

async def main():
    options = ClaudeAgentOptions(
        mcp_servers={
            "filesystem": {
                "command": "npx",
                "args": [
                    "-y",
                    "@modelcontextprotocol/server-filesystem",
                    "/Users/me/projects",
                ],
            }
        },
        allowed_tools=["mcp__filesystem__*"],
    )

    async for message in query(prompt="List files in my project", options=options):
        if isinstance(message, ResultMessage) and message.subtype == "success":
            print(message.result)

asyncio.run(main())

From a config file

Create a .mcp.json file at your project root. The file is picked up when the project setting source is enabled, which it is for default query() options. If you set settingSources explicitly, include "project" for this file to load:

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/Users/me/projects"]
    }
  }
}

Allow MCP tools

MCP tools require explicit permission before Claude can use them. Without permission, Claude will see that tools are available but won't be able to call them.

Tool naming convention

MCP tools follow the naming pattern mcp__<server-name>__<tool-name>. For example, a GitHub server named "github" with a list_issues tool becomes mcp__github__list_issues.

Grant access with allowedTools

Use allowedTools to specify which MCP tools Claude can use:

const _ = {
  options: {
    mcpServers: {
      // your servers
    },
    allowedTools: [
      "mcp__github__*", // All tools from the github server
      "mcp__db__query", // Only the query tool from db server
      "mcp__slack__send_message" // Only send_message from slack server
    ]
  }
};

Wildcards (*) let you allow all tools from a server without listing each one individually.

Prefer allowedTools over permission modes for MCP access. permissionMode: "acceptEdits" does not auto-approve MCP tools (only file edits and filesystem Bash commands). permissionMode: "bypassPermissions" does auto-approve MCP tools but also disables all other safety prompts, which is broader than necessary. A wildcard in allowedTools grants exactly the MCP server you want and nothing more. See Permission modes for a full comparison.

Discover available tools

To see what tools an MCP server provides, check the server's documentation or connect to the server and inspect the system init message:

for await (const message of query({ prompt: "...", options })) {
  if (message.type === "system" && message.subtype === "init") {
    console.log("Available MCP tools:", message.mcp_servers);
  }
}

Transport types

MCP servers communicate with your agent using different transport protocols. Check the server's documentation to see which transport it supports:

• If the docs give you a command to run (like npx @modelcontextprotocol/server-github), use stdio
• If the docs give you a URL, use HTTP or SSE
• If you're building your own tools in code, use an SDK MCP server

stdio servers

Local processes that communicate via stdin/stdout. Use this for MCP servers you run on the same machine:

  ```typescript TypeScript hidelines={1,-1} theme={null}
  const _ = {
    options: {
      mcpServers: {
        github: {
          command: "npx",
          args: ["-y", "@modelcontextprotocol/server-github"],
          env: {
            GITHUB_TOKEN: process.env.GITHUB_TOKEN
          }
        }
      },
      allowedTools: ["mcp__github__list_issues", "mcp__github__search_issues"]
    }
  };
  ```

  ```python Python theme={null}
  options = ClaudeAgentOptions(
      mcp_servers={
          "github": {
              "command": "npx",
              "args": ["-y", "@modelcontextprotocol/server-github"],
              "env": {"GITHUB_TOKEN": os.environ["GITHUB_TOKEN"]},
          }
      },
      allowed_tools=["mcp__github__list_issues", "mcp__github__search_issues"],
  )
  ```




```json theme={null}
{
  "mcpServers": {
    "github": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "env": {
        "GITHUB_TOKEN": "${GITHUB_TOKEN}"
      }
    }
  }
}
```

HTTP/SSE servers

Use HTTP or SSE for cloud-hosted MCP servers and remote APIs:

  ```typescript TypeScript hidelines={1,-1} theme={null}
  const _ = {
    options: {
      mcpServers: {
        "remote-api": {
          type: "sse",
          url: "https://api.example.com/mcp/sse",
          headers: {
            Authorization: `Bearer ${process.env.API_TOKEN}`
          }
        }
      },
      allowedTools: ["mcp__remote-api__*"]
    }
  };
  ```

  ```python Python theme={null}
  options = ClaudeAgentOptions(
      mcp_servers={
          "remote-api": {
              "type": "sse",
              "url": "https://api.example.com/mcp/sse",
              "headers": {"Authorization": f"Bearer {os.environ['API_TOKEN']}"},
          }
      },
      allowed_tools=["mcp__remote-api__*"],
  )
  ```




```json theme={null}
{
  "mcpServers": {
    "remote-api": {
      "type": "sse",
      "url": "https://api.example.com/mcp/sse",
      "headers": {
        "Authorization": "Bearer ${API_TOKEN}"
      }
    }
  }
}
```

For HTTP (non-streaming), use "type": "http" instead.

SDK MCP servers

Define custom tools directly in your application code instead of running a separate server process. See the custom tools guide for implementation details.

MCP tool search

When you have many MCP tools configured, tool definitions can consume a significant portion of your context window. Tool search solves this by withholding tool definitions from context and loading only the ones Claude needs for each turn.

Tool search is enabled by default. See Tool search for configuration options and details.

For more detail, including best practices and using tool search with custom SDK tools, see the tool search guide.

Authentication

Most MCP servers require authentication to access external services. Pass credentials through environment variables in the server configuration.

Pass credentials via environment variables

Use the env field to pass API keys, tokens, and other credentials to the MCP server:

  ```typescript TypeScript hidelines={1,-1} theme={null}
  const _ = {
    options: {
      mcpServers: {
        github: {
          command: "npx",
          args: ["-y", "@modelcontextprotocol/server-github"],
          env: {
            GITHUB_TOKEN: process.env.GITHUB_TOKEN
          }
        }
      },
      allowedTools: ["mcp__github__list_issues"]
    }
  };
  ```

  ```python Python theme={null}
  options = ClaudeAgentOptions(
      mcp_servers={
          "github": {
              "command": "npx",
              "args": ["-y", "@modelcontextprotocol/server-github"],
              "env": {"GITHUB_TOKEN": os.environ["GITHUB_TOKEN"]},
          }
      },
      allowed_tools=["mcp__github__list_issues"],
  )
  ```




```json theme={null}
{
  "mcpServers": {
    "github": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "env": {
        "GITHUB_TOKEN": "${GITHUB_TOKEN}"
      }
    }
  }
}
```

The `${GITHUB_TOKEN}` syntax expands environment variables at runtime.

See List issues from a repository for a complete working example with debug logging.

HTTP headers for remote servers

For HTTP and SSE servers, pass authentication headers directly in the server configuration:

  ```typescript TypeScript hidelines={1,-1} theme={null}
  const _ = {
    options: {
      mcpServers: {
        "secure-api": {
          type: "http",
          url: "https://api.example.com/mcp",
          headers: {
            Authorization: `Bearer ${process.env.API_TOKEN}`
          }
        }
      },
      allowedTools: ["mcp__secure-api__*"]
    }
  };
  ```

  ```python Python theme={null}
  options = ClaudeAgentOptions(
      mcp_servers={
          "secure-api": {
              "type": "http",
              "url": "https://api.example.com/mcp",
              "headers": {"Authorization": f"Bearer {os.environ['API_TOKEN']}"},
          }
      },
      allowed_tools=["mcp__secure-api__*"],
  )
  ```




```json theme={null}
{
  "mcpServers": {
    "secure-api": {
      "type": "http",
      "url": "https://api.example.com/mcp",
      "headers": {
        "Authorization": "Bearer ${API_TOKEN}"
      }
    }
  }
}
```

The `${API_TOKEN}` syntax expands environment variables at runtime.

OAuth2 authentication

The MCP specification supports OAuth 2.1 for authorization. The SDK doesn't handle OAuth flows automatically, but you can pass access tokens via headers after completing the OAuth flow in your application:

// After completing OAuth flow in your app
const accessToken = await getAccessTokenFromOAuthFlow();

const options = {
  mcpServers: {
    "oauth-api": {
      type: "http",
      url: "https://api.example.com/mcp",
      headers: {
        Authorization: `Bearer ${accessToken}`
      }
    }
  },
  allowedTools: ["mcp__oauth-api__*"]
};

# After completing OAuth flow in your app
access_token = await get_access_token_from_oauth_flow()

options = ClaudeAgentOptions(
    mcp_servers={
        "oauth-api": {
            "type": "http",
            "url": "https://api.example.com/mcp",
            "headers": {"Authorization": f"Bearer {access_token}"},
        }
    },
    allowed_tools=["mcp__oauth-api__*"],
)

Examples

List issues from a repository

This example connects to the GitHub MCP server to list recent issues. The example includes debug logging to verify the MCP connection and tool calls.

Before running, create a [GitHub personal access token](https://github.com/setti