# MCP + FastAPI demo

Small example showing how a normal FastAPI REST API becomes an MCP server
that an LLM client (Claude Desktop, Claude Code, etc.) can call as tools.

## What's here

- `main.py` — a tiny "Tasks" REST API (`/tasks`, `/tasks/{id}`, ...) built
  with plain FastAPI, plus 3 lines at the bottom that wrap it with
  [`fastapi-mcp`](https://github.com/tadata-org/fastapi-mcp).
- `fastapi-mcp` introspects your routes (via their `operation_id`) and
  auto-generates an MCP tool for each one — no separate tool definitions
  to hand-write. It mounts an MCP endpoint at `/mcp` alongside your
  normal REST routes.

## How MCP fits in

MCP (Model Context Protocol) is a standard way for an LLM client to
discover and call "tools" exposed by a server. Normally you'd hand-write
a tool schema for each capability. `fastapi-mcp` skips that by reusing
the OpenAPI schema FastAPI already generates from your Pydantic models
and route signatures — so each REST endpoint becomes both a normal HTTP
route *and* an MCP tool, for free.

## Run it

```bash
cd ~/mcp-fastapi-demo
python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt
uvicorn main:app --reload
```

- REST API + docs: http://127.0.0.1:8000/docs
- MCP endpoint: http://127.0.0.1:8000/mcp

## Try it as a normal REST API first

```bash
curl -X POST http://127.0.0.1:8000/tasks -H 'Content-Type: application/json' -d '{"title": "learn MCP"}'
curl http://127.0.0.1:8000/tasks
```

## Connect an MCP client

### Option A: MCP Inspector (fastest way to poke at it)

```bash
npx @modelcontextprotocol/inspector
```

Point it at `http://127.0.0.1:8000/mcp` as an SSE/HTTP server and you'll
see `list_tasks`, `create_task`, `get_task`, `complete_task`,
`delete_task` show up as callable tools — one per FastAPI route.

### Option B: Claude Desktop

Add to your Claude Desktop MCP config (`claude_desktop_config.json`):

```json
{
  "mcpServers": {
    "tasks": {
      "url": "http://127.0.0.1:8000/mcp"
    }
  }
}
```

Restart Claude Desktop, and you should be able to ask it to list/create
tasks — it'll call your FastAPI endpoints under the hood.

## Key takeaway

`operation_id` in each `@app.get/post/...` decorator becomes the MCP
tool name, and the `summary` becomes its description. Add a new FastAPI
route with an `operation_id` and it automatically becomes a new MCP tool
— that's the whole trick.