MCPサーバーとは｜実装の中身と事例で見る振る舞い

{
  "jsonrpc": "2.0",
  "id": 42,
  "method": "tools/call",
  "params": {
    "name": "search_customer",
    "arguments": { "query": "山田" }
  }
}

{
  "jsonrpc": "2.0",
  "id": 42,
  "result": {
    "content": [
      { "type": "text", "text": "顧客ID:1023, 名前:山田太郎" }
    ]
  }
}

-> client to server
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "initialize",
  "params": {
    "protocolVersion": "2025-11-25",
    "capabilities": {},
    "clientInfo": { "name": "claude-desktop", "version": "0.7.0" }
  }
}

<- server to client
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "protocolVersion": "2025-11-25",
    "capabilities": {
      "tools": {},
      "resources": {},
      "prompts": {}
    },
    "serverInfo": { "name": "crm-mcp", "version": "1.0.0" }
  }
}

-> client to server
{ "jsonrpc": "2.0", "id": 2, "method": "tools/list" }

<- server to client
{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "tools": [
      {
        "name": "search_customer",
        "description": "顧客名やメールから顧客レコードを検索する（読み取り専用）",
        "inputSchema": {
          "type": "object",
          "properties": {
            "query": { "type": "string" }
          },
          "required": ["query"]
        }
      }
    ]
  }
}

-> client to server
{
  "jsonrpc": "2.0",
  "id": 3,
  "method": "tools/call",
  "params": {
    "name": "search_customer",
    "arguments": { "query": "山田 太郎" }
  }
}

<- server to client
{
  "jsonrpc": "2.0",
  "id": 3,
  "result": {
    "content": [
      { "type": "text", "text": "顧客ID:1023 / 山田太郎 / yamada@example.com" }
    ],
    "isError": false
  }
}

import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import {
  CallToolRequestSchema,
  ListToolsRequestSchema,
} from "@modelcontextprotocol/sdk/types.js";

const server = new Server(
  { name: "crm-mcp", version: "1.0.0" },
  { capabilities: { tools: {} } },
);

// ツール一覧を返す
server.setRequestHandler(ListToolsRequestSchema, async () => ({
  tools: [
    {
      name: "search_customer",
      description: "顧客名やメールから顧客レコードを検索する（読み取り専用）",
      inputSchema: {
        type: "object",
        properties: { query: { type: "string" } },
        required: ["query"],
      },
    },
  ],
}));

// ツール実行
server.setRequestHandler(CallToolRequestSchema, async (req) => {
  const { name, arguments: args } = req.params;
  if (name !== "search_customer") {
    return { content: [{ type: "text", text: "unknown tool" }], isError: true };
  }
  const query = args?.query ?? "";
  // ここで実際の CRM API を叩く（疑似コード）
  const hit = await crm.findByQuery(query);
  return {
    content: [{ type: "text", text: `顧客ID:${hit.id} / ${hit.name}` }],
    isError: false,
  };
});

// stdio で起動
const transport = new StdioServerTransport();
await server.connect(transport);