MCP Server Building Skill

You now have expertise in building MCP (Model Context Protocol) servers. MCP enables Claude to interact with external services through a standardized protocol.

What is MCP?

MCP servers expose:

• Tools: Functions Claude can call (like API endpoints)

• Resources: Data Claude can read (like files or database records)

• Prompts: Pre-built prompt templates

Quick Start: Python MCP Server

1. Project Setup

Create project

mkdir my-mcp-server && cd my-mcp-server python3 -m venv venv && source venv/bin/activate

Install MCP SDK

pip install mcp

2. Basic Server Template

#!/usr/bin/env python3 """my_server.py - A simple MCP server"""

from mcp.server import Server from mcp.server.stdio import stdio_server from mcp.types import Tool, TextContent

Create server instance

server = Server("my-server")

Define a tool

@server.tool() async def hello(name: str) -> str: """Say hello to someone.

Args:
    name: The name to greet
"""
return f"Hello, {name}!"

@server.tool() async def add_numbers(a: int, b: int) -> str: """Add two numbers together.

Args:
    a: First number
    b: Second number
"""
return str(a + b)

Run server

async def main(): async with stdio_server() as (read, write): await server.run(read, write)

if name == "main": import asyncio asyncio.run(main())

3. Register with Claude

Add to ~/.claude/mcp.json :

{ "mcpServers": { "my-server": { "command": "python3", "args": ["/path/to/my_server.py"] } } }

TypeScript MCP Server

1. Setup

mkdir my-mcp-server && cd my-mcp-server npm init -y npm install @modelcontextprotocol/sdk

2. Template

// src/index.ts 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 tools server.setRequestHandler("tools/list", async () => ({ tools: [ { name: "hello", description: "Say hello to someone", inputSchema: { type: "object", properties: { name: { type: "string", description: "Name to greet" }, }, required: ["name"], }, }, ], }));

server.setRequestHandler("tools/call", async (request) => { if (request.params.name === "hello") { const name = request.params.arguments.name; return { content: [{ type: "text", text: Hello, ${name}! }] }; } throw new Error("Unknown tool"); });

// Start server const transport = new StdioServerTransport(); server.connect(transport);

Advanced Patterns

External API Integration

import httpx from mcp.server import Server

server = Server("weather-server")

@server.tool() async def get_weather(city: str) -> str: """Get current weather for a city.""" async with httpx.AsyncClient() as client: resp = await client.get( f"https://api.weatherapi.com/v1/current.json", params={"key": "YOUR_API_KEY", "q": city} ) data = resp.json() return f"{city}: {data['current']['temp_c']}C, {data['current']['condition']['text']}"

Database Access

import sqlite3 from mcp.server import Server

server = Server("db-server")

@server.tool() async def query_db(sql: str) -> str: """Execute a read-only SQL query.""" if not sql.strip().upper().startswith("SELECT"): return "Error: Only SELECT queries allowed"

conn = sqlite3.connect("data.db")
cursor = conn.execute(sql)
rows = cursor.fetchall()
conn.close()
return str(rows)

Resources (Read-only Data)

@server.resource("config://settings") async def get_settings() -> str: """Application settings.""" return open("settings.json").read()

@server.resource("file://{path}") async def read_file(path: str) -> str: """Read a file from the workspace.""" return open(path).read()

Testing

Test with MCP Inspector

npx @anthropics/mcp-inspector python3 my_server.py

Or send test messages directly

echo '{"jsonrpc":"2.0","id":1,"method":"tools/list"}' | python3 my_server.py

Best Practices

• Clear tool descriptions: Claude uses these to decide when to call tools

• Input validation: Always validate and sanitize inputs

• Error handling: Return meaningful error messages

• Async by default: Use async/await for I/O operations

• Security: Never expose sensitive operations without auth

• Idempotency: Tools should be safe to retry