MCP (Model Context Protocol)

エンジニアのためのWebチートシート

MCPは2層構成です。

┌─────────────────────────────┐
│        MCP Host             │
│  (Claude Desktop, VS Code)  │
│                             │
│  ┌──────────┐ ┌──────────┐  │
│  │ Client 1 │ │ Client 2 │  │
│  └────┬─────┘ └────┬─────┘  │
└───────┼────────────┼────────┘
        │            │
   ┌────┴────┐  ┌────┴────┐
   │ Server  │  │ Server  │
   │ (Local) │  │(Remote) │
   └─────────┘  └─────────┘

Data Layer:
  - Lifecycle (init, capability negotiation)
  - Server: Tools, Resources, Prompts
  - Client: Sampling, Elicitation

Transport Layer:
  - Stdio (local)
  - Streamable HTTP (remote)

FastMCPフレームワークを使ったTypeScript実装です。

import { FastMCP } from "fastmcp";
import { z } from "zod";

const server = new FastMCP({
  name: "My MCP Server",
  version: "1.0.0",
});

// Tool definition
server.addTool({
  name: "calculate",
  description: "Perform a calculation",
  parameters: z.object({ expression: z.string() }),
  execute: async (args) => String(eval(args.expression)),
});

// Resource definition
server.addResource({
  uri: "config://app",
  name: "App Configuration",
  mimeType: "application/json",
  async load() {
    return { text: JSON.stringify({ debug: true }) };
  },
});

// Prompt definition
server.addPrompt({
  name: "code-review",
  description: "Code review prompt",
  arguments: [{ name: "code", required: true }],
  load: async (args) =>
    `Review the following code:\n${args.code}`,
});

server.start({ transportType: "stdio" });

@modelcontextprotocol/sdk を使った低レベル実装です。

import { McpServer } from
  "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from
  "@modelcontextprotocol/sdk/server/stdio.js";

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

// Tool
server.tool("get-weather", "Get weather",
  { city: { type: "string" } },
  async ({ city }) => ({
    content: [{ type: "text",
      text: `Weather in ${city}: Sunny` }],
  })
);

// Resource
server.resource("docs", "docs://readme",
  async (uri) => ({
    contents: [{ uri: uri.href,
      text: "# Docs", mimeType: "text/markdown" }],
  })
);

const transport = new StdioServerTransport();
await server.connect(transport);

デコレーターベースのPython実装です。

from fastmcp import FastMCP

mcp = FastMCP("My MCP Server")

@mcp.tool()
def calculate(expression: str) -> str:
    """Evaluate a math expression"""
    return str(eval(expression))

@mcp.tool()
def search_database(
    query: str,
    limit: int = 10
) -> list[dict]:
    """Search the database"""
    # DB query logic here
    return [{"id": 1, "name": "Result"}]

@mcp.resource("config://app")
def get_config() -> str:
    """Get application configuration"""
    return '{"debug": true, "version": "1.0"}'

@mcp.prompt()
def code_review(code: str) -> str:
    """Generate a code review prompt"""
    return f"Review this code:\n{code}"

if __name__ == "__main__":
    mcp.run()  # Default: stdio transport

mcp パッケージを使った低レベル実装です。

from mcp.server import Server
from mcp.server.stdio import stdio_server
import mcp.types as types

server = Server("my-server")

@server.list_tools()
async def list_tools():
    return [types.Tool(
        name="get-weather",
        description="Get weather",
        inputSchema={"type": "object",
          "properties": {"city": {"type": "string"}},
          "required": ["city"]},
    )]

@server.call_tool()
async def call_tool(name: str, arguments: dict):
    if name == "get-weather":
        return [types.TextContent(
            type="text",
            text=f"Weather: Sunny in {arguments['city']}"
        )]

async def main():
    async with stdio_server() as (r, w):
        await server.run(r, w,
            server.create_initialization_options())

import asyncio
asyncio.run(main())

MCPクライアントの設定ファイルの場所です。

# macOS (Claude Desktop)
~/Library/Application Support/Claude/claude_desktop_config.json

# Windows (Claude Desktop)
%APPDATA%\Claude\claude_desktop_config.json

# Claude Code
.claude/settings.json  # or ~/.claude/settings.json

ローカルで実行するサーバーの設定例です。

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": [
        "-y",
        "@modelcontextprotocol/server-filesystem",
        "/Users/me/projects"
      ]
    },
    "github": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "env": {
        "GITHUB_TOKEN": "${GITHUB_TOKEN}"
      }
    },
    "python-server": {
      "command": "python",
      "args": ["-m", "my_mcp_server"],
      "env": {
        "API_KEY": "${API_KEY}"
      }
    }
  }
}

リモートで実行するサーバーの設定例です。

{
  "mcpServers": {
    "remote-api": {
      "type": "http",
      "url": "https://api.example.com/mcp",
      "headers": {
        "Authorization": "Bearer ${API_KEY}"
      }
    }
  }
}

1. Client → Server: Initialize Request

{
  "jsonrpc": "2.0", "id": 1,
  "method": "initialize",
  "params": {
    "protocolVersion": "2025-03-26",
    "capabilities": { "sampling": {} },
    "clientInfo": { "name": "Claude Desktop", "version": "1.0.0" }
  }
}

2. Server → Client: Initialize Response

{
  "jsonrpc": "2.0", "id": 1,
  "result": {
    "protocolVersion": "2025-03-26",
    "capabilities": { "tools": { "listChanged": true } },
    "serverInfo": { "name": "My Server", "version": "1.0.0" }
  }
}

3. Client → Server: Initialized Notification

{ "jsonrpc": "2.0", "method": "notifications/initialized" }

Request

{
  "jsonrpc": "2.0", "id": "req-1",
  "method": "tools/call",
  "params": { "name": "calculate",
    "arguments": { "expression": "2 + 2" } }
}

Success Response

{
  "jsonrpc": "2.0", "id": "req-1",
  "result": {
    "content": [{ "type": "text", "text": "4" }]
  }
}

Error Response / Notification

// Error
{ "jsonrpc": "2.0", "id": "req-1",
  "error": { "code": -32600, "message": "Invalid Request" } }

// Notification (no id, no response)
{ "jsonrpc": "2.0",
  "method": "notifications/tools/list_changed" }