┌────────────────────┐         ┌─────────────────────┐
│   MCP Client       │ ◄─────► │   MCP Server        │
│  (Claude / Cursor) │  JSON   │  (あなたが構築)     │
│                    │  -RPC   │                     │
└────────────────────┘         └─────────────────────┘
                                        │
                          ┌─────────────┼─────────────┐
                          ▼             ▼             ▼
                       Tools       Resources      Prompts
                    (アクション)   (データ読取)  (テンプレート)

python -m venv .venv
source .venv/bin/activate
pip install mcp

npm init -y
npm install @modelcontextprotocol/sdk

my-mcp-server/
├── server.py
├── tools/
│   ├── calculator.py
│   └── web_search.py
├── resources/
│   └── file_reader.py
├── prompts/
│   └── templates.py
├── tests/
│   └── test_tools.py
└── pyproject.toml

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("my-first-server")

@mcp.tool()
def say_hello(name: str) -> str:
    return f"Hello, {name}! これが最初の MCP ツールです。"

if __name__ == "__main__":
    mcp.run()

python server.py
npx @modelcontextprotocol/inspector python server.py

from pydantic import BaseModel, Field

class SearchInput(BaseModel):
    query: str = Field(description="検索キーワード")
    max_results: int = Field(default=5, description="最大件数")
    language: str = Field(default="ja", description="結果言語")

@mcp.tool()
def web_search(input: SearchInput) -> list[dict]:
    ...

import httpx

@mcp.tool()
async def fetch_url(url: str) -> str:
    async with httpx.AsyncClient(timeout=30.0) as client:
        response = await client.get(url)
        response.raise_for_status()
        return response.text

@mcp.resource("config://app-settings")
def get_app_settings() -> str:
    return json.dumps({"version": "1.0", "env": "production"})

@mcp.resource("user://{user_id}/profile")
def get_user_profile(user_id: str) -> str:
    user = db.query_user(user_id)
    return json.dumps(user)

from mcp.types import PromptMessage, TextContent

@mcp.prompt()
def code_review_prompt(language: str, code: str) -> list[PromptMessage]:
    return [
        PromptMessage(
            role="user",
            content=TextContent(
                type="text",
                text=f"次の {language} コードをバグ・セキュリティ・性能の観点でレビューしてください:\n```{language}\n{code}\n```"
            )
        )
    ]

mcp = FastMCP("remote-server", transport="streamable-http")

if __name__ == "__main__":
    mcp.run(host="0.0.0.0", port=8000)

import pytest
from mcp.client.session import ClientSession
from mcp.client.stdio import StdioServerParameters, stdio_client

@pytest.mark.asyncio
async def test_calculator_tool():
    server_params = StdioServerParameters(
        command="python",
        args=["server.py"]
    )
    async with stdio_client(server_params) as (read, write):
        async with ClientSession(read, write) as session:
            await session.initialize()
            result = await session.call_tool("calculate", {"expression": "2 + 2"})
            assert result.content[0].text == "4"