​
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.

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Configuration

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Basic Configuration

Configure MCP servers in .mcp.json at your project root: 
{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["@modelcontextprotocol/server-filesystem"],
      "env": {
        "ALLOWED_PATHS": "/Users/me/projects"
      }
    }
  }
}

​
Using MCP Servers in SDK

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

for await (const message of query({
  prompt: "List files in my project",
  options: {
    mcpConfig: ".mcp.json",
    allowedTools: ["mcp__filesystem__list_files"]
  }
})) {
  if (message.type === "result" && message.subtype === "success") {
    console.log(message.result);
  }
}

​
Transport Types

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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:

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Resource Management

MCP servers can expose resources that Claude can list and read: 
import { query } from "@anthropic-ai/claude-code";

// List available resources
for await (const message of query({
  prompt: "What resources are available from the database server?",
  options: {
    mcpConfig: ".mcp.json",
    allowedTools: ["mcp__list_resources", "mcp__read_resource"]
  }
})) {
  if (message.type === "result") console.log(message.result);
}

​
Authentication

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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.

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Error Handling

Handle MCP connection failures gracefully: 
import { query } from "@anthropic-ai/claude-code";

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");
  }
}