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name: mcp-builder category: mcp version: 1.0.0 description: Build custom Model Context Protocol servers to extend Claude's capabilities author: anthropics/skills verified: true tags: [mcp, integration, development, api]

MCP Builder

Overview

Create high-quality Model Context Protocol (MCP) servers that integrate Claude with external tools, APIs, and data sources.

When to Use This Skill

✅ Building custom tool integrations for Claude ✅ Connecting Claude to internal APIs or databases ✅ Creating reusable Claude capabilities ✅ Extending Claude with external data sources

MCP Server Structure

Basic Package Structure

Copymy-mcp-server/
├── package.json
├── tsconfig.json
├── src/
│   ├── index.ts      # Main server entry point
│   └── tools/        # Tool implementations
└── README.md

Minimal Server Example

Copyimport { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";

const server = new Server({
  name: "my-server",
  version: "1.0.0"
});

// Define a tool
server.setRequestHandler(CallToolRequestSchema, async (request) => {
  if (request.params.name === "my-tool") {
    return {
      content: [{
        type: "text",
        text: "Tool result here"
      }]
    };
  }
});

// List available tools
server.setRequestHandler(ListToolsRequestSchema, async () => {
  return {
    tools: [{
      name: "my-tool",
      description: "Does something useful",
      inputSchema: {
        type: "object",
        properties: {
          param: { type: "string" }
        }
      }
    }]
  };
});

async function main() {
  const transport = new StdioServerTransport();
  await server.connect(transport);
}

main().catch(console.error);

Best Practices

Tool Design

• Single responsibility: Each tool does one thing well
• Clear inputs: Use JSON Schema for validation
• Helpful errors: Return actionable error messages
• Idempotent when possible: Safe to retry

Error Handling

Copytry {
  const result = await externalApiCall(params);
  return { content: [{ type: "text", text: result }] };
} catch (error) {
  return {
    content: [{
      type: "text",
      text: `Error: ${error.message}. Check API key and permissions.`
    }],
    isError: true
  };
}

Resource Management

• Close connections properly
• Use timeouts for external calls
• Handle rate limiting gracefully
• Log important operations

Common MCP Patterns

API Integration

Copy// Weather API example
server.setRequestHandler(CallToolRequestSchema, async (request) => {
  if (request.params.name === "get-weather") {
    const location = request.params.arguments?.location;
    const weather = await weatherAPI.get(location);
    return {
      content: [{
        type: "text",
        text: `Weather in ${location}: ${weather.temp}°F`
      }]
    };
  }
});

Database Queries

Copy// Database query example
server.setRequestHandler(CallToolRequestSchema, async (request) => {
  if (request.params.name === "query-db") {
    const query = request.params.arguments?.query;
    const results = await db.execute(query);
    return {
      content: [{
        type: "text",
        text: JSON.stringify(results, null, 2)
      }]
    };
  }
});

Testing Your MCP Server

Manual Testing

Copy# Run server
node build/index.js

# Test from Claude Code
# "Use the get-weather tool for San Francisco"

Integration Testing

Create test configuration in MCP client settings:

Copy{
  "mcpServers": {
    "my-server": {
      "command": "node",
      "args": ["/path/to/server/build/index.js"]
    }
  }
}

Security Considerations

• Validate all input parameters
• Sanitize data before external API calls
• Use environment variables for secrets
• Implement rate limiting
• Never log sensitive data
• Use authentication for protected resources

Integration with Claude

When building MCP servers, say:

• "Help me create an MCP server for [API/service]"
• "Add a tool to my MCP server that [does X]"
• "Debug my MCP server implementation"

Claude will:

• Structure the server correctly
• Implement tool handlers
• Add proper error handling
• Write JSON Schema for inputs
• Create documentation