AIエージェントとシステムをつなぐMCP入門（stdio実装編）

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

// サーバーのインスタンス化
const server = new McpServer({
  name: "hello-world-server",
  version: "1.0.0",
});

// ツールの登録
server.registerTool(
  "hello",
  {
    title: "hello, world!",
    inputSchema: { name: z.string().describe("メッセージに追加する名前") }, // 入力スキーマの定義
    outputSchema: { message: z.string().describe("メッセージ") }, // 出力スキーマの定義
  },
  async ({ name }) => {
    return {
      content: [{ type: "text", text: `Hello, ${name}!` }], // デフォルトのレスポンス
      structuredContent: { message: `Hello, ${name}!` }, // 出力スキーマに基づくレスポンス
    };
  },
);

// 起動処理
async function boot() {
  const transport = new StdioServerTransport();
  await server.connect(transport);
  console.error("MCP Hello World Server (Modern) running on stdio"); // 標準出力にログを出力するとエラーになるため、`console.error`を使用しています
}

try {
  await boot();
} catch (error) {
  console.error("Fatal error:", error);
  process.exit(1);
}

server.registerTool(
  `output_log`,
  { title: 'output_log' },
  async () => {
    console.log('debug log'); // to stdout
    console.info('info log'); // to stdout
    console.warn('warn log'); // to stderr
    console.error('error log'); // to stderr
    return { content: [{ type: "text", text: 'output log tool' }] };
  },
);

Received POST message for sessionId xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxx1xx
Error from MCP server: SyntaxError: Unexpected token 'd', "debug log" is not valid JSON
    at JSON.parse (<anonymous>)
    at deserializeMessage (file:///C:/Users/~/shared/stdio.js:26:44)
    at ReadBuffer.readMessage (file:///C:/Users/~/shared/stdio.js:19:16)
    at StdioClientTransport.processReadBuffer (file:///C:/Users/~/client/stdio.js:126:50)
    at Socket.<anonymous> (file:///C:/Users/~/client/stdio.js:92:22)
    at Socket.emit (node:events:519:28)
    at addChunk (node:internal/streams/readable:561:12)
    at readableAddChunkPushByteMode (node:internal/streams/readable:512:3)
    at Readable.push (node:internal/streams/readable:392:5)
    at Pipe.onStreamRead (node:internal/stream_base_commons:189:23)
Error from MCP server: SyntaxError: Unexpected token 'i', "info log" is not valid JSON
    at JSON.parse (<anonymous>)
    at deserializeMessage (file:///C:/Users/~/shared/stdio.js:26:44)
    at ReadBuffer.readMessage (file:///C:/Users/~/shared/stdio.js:19:16)
    at StdioClientTransport.processReadBuffer (file:///C:/Users/~/client/stdio.js:126:50)
    at Socket.<anonymous> (file:///C:/Users/~/client/stdio.js:92:22)
    at Socket.emit (node:events:519:28)
    at addChunk (node:internal/streams/readable:561:12)
    at readableAddChunkPushByteMode (node:internal/streams/readable:512:3)
    at Readable.push (node:internal/streams/readable:392:5)
    at Pipe.onStreamRead (node:internal/stream_base_commons:189:23)