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

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

Minimal Server Example

import { 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

try {
  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

// 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

// 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

# 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:

{
  "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

mcp-builder

Installation

Details

Usage

Skill Instructions