Guides

MCP in the SDK

Extend Claude Code with custom tools using Model Context Protocol servers

Overview

Model Context Protocol (MCP) servers extend Claude Code with custom tools and capabilities. MCPs can run as external processes, connect via HTTP/SSE, or execute directly within your SDK application.

Configuration

Basic Configuration

Configure MCP servers in .mcp.json at your project root:

TypeScript

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

Python

{
  "mcpServers": {
    "filesystem": {
      "command": "python",
      "args": ["-m", "mcp_server_filesystem"],
      "env": {
        "ALLOWED_PATHS": "/Users/me/projects"
      }
    }
  }
}

Using MCP Servers in SDK

import { query } from "@anthropic-ai/claude-agent-sdk";

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

Transport Types

stdio Servers

External processes communicating via stdin/stdout:

// .mcp.json configuration
{
  "mcpServers": {
    "my-tool": {
      "command": "node",
      "args": ["./my-mcp-server.js"],
      "env": {
        "DEBUG": "${DEBUG:-false}"
      }
    }
  }
}

HTTP/SSE Servers

Remote servers with network communication:

// SSE server configuration
{
  "mcpServers": {
    "remote-api": {
      "type": "sse",
      "url": "https://api.example.com/mcp/sse",
      "headers": {
        "Authorization": "Bearer ${API_TOKEN}"
      }
    }
  }
}

// HTTP server configuration
{
  "mcpServers": {
    "http-service": {
      "type": "http",
      "url": "https://api.example.com/mcp",
      "headers": {
        "X-API-Key": "${API_KEY}"
      }
    }
  }
}

SDK MCP Servers

In-process servers running within your application. For detailed information on creating custom tools, see the Custom Tools guide:

Resource Management

MCP servers can expose resources that Claude can list and read:

import { query } from "@anthropic-ai/claude-agent-sdk";

// List available resources
for await (const message of query({
  prompt: "What resources are available from the database server?",
  options: {
    mcpServers: {
      "database": {
        command: "npx",
        args: ["@modelcontextprotocol/server-database"]
      }
    },
    allowedTools: ["mcp__list_resources", "mcp__read_resource"]
  }
})) {
  if (message.type === "result") console.log(message.result);
}

Authentication

Environment Variables

// .mcp.json with environment variables
{
  "mcpServers": {
    "secure-api": {
      "type": "sse",
      "url": "https://api.example.com/mcp",
      "headers": {
        "Authorization": "Bearer ${API_TOKEN}",
        "X-API-Key": "${API_KEY:-default-key}"
      }
    }
  }
}

// Set environment variables
process.env.API_TOKEN = "your-token";
process.env.API_KEY = "your-key";

OAuth2 Authentication

OAuth2 MCP authentication in-client is not currently supported.

Error Handling

Handle MCP connection failures gracefully:

import { query } from "@anthropic-ai/claude-agent-sdk";

for await (const message of query({
  prompt: "Process data",
  options: {
    mcpServers: {
      "data-processor": dataServer
    }
  }
})) {
  if (message.type === "system" && message.subtype === "init") {
    // Check MCP server status
    const failedServers = message.mcp_servers.filter(
      s => s.status !== "connected"
    );
    
    if (failedServers.length > 0) {
      console.warn("Failed to connect:", failedServers);
    }
  }
  
  if (message.type === "result" && message.subtype === "error_during_execution") {
    console.error("Execution failed");
  }
}

Related Resources

Custom Tools Guide - Detailed guide on creating SDK MCP servers
TypeScript SDK Reference
Python SDK Reference
SDK Permissions
Common Workflows