Claude Code: MCP (Model Context Protocol)

# MCP なし：手動データベースクエリ
> Check how many records are in the users table
Claude Code: データベースに直接アクセスできません。以下を実行：
  psql -c "SELECT COUNT(*) FROM users"

# MCP あり（PostgreSQL Server）：直接クエリ
> Check how many records are in the users table
Claude Code: [PostgreSQL MCP 経由でクエリ]
  users テーブルには 12,450 レコードがあります。
  アクティブユーザー：8,920（71.6%）、
  過去7日間の登録：342。

// ~/.claude/mcp_settings.json
{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-filesystem", "/home/user/projects"]
    },
    "postgres": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-postgres"],
      "env": {
        "DATABASE_URL": "postgresql://user:pass@localhost:5432/mydb"
      }
    }
  }
}

// .claude/mcp_settings.json
{
  "mcpServers": {
    "github": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-github"],
      "env": {
        "GITHUB_TOKEN": "ghp_xxxxx"
      }
    }
  }
}

> Query user registrations in the last 7 days, grouped by day

Claude Code: [PostgreSQL MCP を使用]
  → SQL クエリを実行中...
  Results: 7日間の内訳と日別カウント

import { Server } from "@anthropic/mcp";

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

server.tool("get_weather", "Get current weather for a city", {
  city: { type: "string", description: "City name" },
}, async ({ city }) => {
  const response = await fetch(
    `https://api.weather.com/current?city=${city}`
  );
  const data = await response.json();
  return {
    content: [{
      type: "text",
      text: `${city}: ${data.temperature}°C, ${data.condition}`
    }]
  };
});

server.start();