MCPサーバーを作ってみる

cd ~/workspace
mkdir hello-mcp-server
cd hello-mcp-server
npm init -y
pnpm install @modelcontextprotocol/sdk zod
pnpm install -D @types/node typescript
mkdir src
touch src/index.ts

{
  "type": "module",
  "bin": {
    "weather": "./build/index.js"
  },
  "scripts": {
    "build": "tsc && chmod 755 build/index.js"
  },
  "files": [
    "build"
  ],
}

touch tsconfig.json

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "Node16",
    "moduleResolution": "Node16",
    "outDir": "./build",
    "rootDir": "./src",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules"]
}

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

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

server.tool(
	"double_number",
	"与えられた数値を2倍にする",
	{
		num: z.number().describe("数値"),
	},
	({ num }) => ({
		content: [
			{
				type: "text",
				text: (num * 2).toString(),
			},
		],
	}),
);

async function main() {
	const transport = new StdioServerTransport();
	await server.connect(transport);
	console.error("Weather MCP Server running on stdio");
}

main().catch((error) => {
	console.error("Fatal error in main():", error);
	process.exit(1);
});

pnpm add --save-dev --save-exact @biomejs/biome
pnpm biome init

pnpm build

node build/index.js

Weather MCP Server running on stdio

code ~/Library/Application\ Support/Claude/claude_desktop_config.json

{
    "mcpServers": {
        "weather": {
            "command": "node",
            "args": [
                "/Users/susukida/workspace/hello-mcp-server/build/index.js"
            ]
        }
    }
}

2025-05-05T06:24:10.835Z [weather] [info] Initializing server...
2025-05-05T06:24:10.859Z [weather] [info] Server started and connected successfully
2025-05-05T06:24:10.894Z [weather] [info] Message from client: {"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"claude-ai","version":"0.1.0"}},"jsonrpc":"2.0","id":0}
/Users/susukida/workspace/hello-mcp-server/build/index.js:1
import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
       ^

SyntaxError: Unexpected token {
    at Module._compile (internal/modules/cjs/loader.js:760:23)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:827:10)
    at Module.load (internal/modules/cjs/loader.js:685:32)
    at Function.Module._load (internal/modules/cjs/loader.js:620:12)
    at Function.Module.runMain (internal/modules/cjs/loader.js:877:12)
    at internal/main/run_main_module.js:21:11
2025-05-05T06:24:11.107Z [weather] [info] Server transport closed
2025-05-05T06:24:11.108Z [weather] [info] Client transport closed
2025-05-05T06:24:11.108Z [weather] [info] Server transport closed unexpectedly, this is likely due to the process exiting early. If you are developing this MCP server you can add output to stderr (i.e. `console.error('...')` in JavaScript, `print('...', file=sys.stderr)` in python) and it will appear in this log.
2025-05-05T06:24:11.108Z [weather] [error] Server disconnected. For troubleshooting guidance, please visit our [debugging documentation](https://modelcontextprotocol.io/docs/tools/debugging) {"context":"connection"}
2025-05-05T06:24:11.108Z [weather] [info] Client transport closed

{
	"mcpServers": {
		"weather": {
			"command": "/Users/susukida/.nvm/versions/node/v20.15.1/bin/node",
			"args": ["/Users/susukida/workspace/hello-mcp-server/build/index.js"]
		}
	}
}

nvm ls --no-colors | grep -o "v[0-9.]\+"

double_number を使って 3 を 2 倍にした結果を表示してください