Orders Server

A small practice project to learn how the Model Context Protocol (MCP) works. It exposes an in-memory “orders” API as MCP tools so an MCP client (e.g. Cursor) can create and list orders via the protocol.

What’s in this repo

• app/ — Core domain: Pydantic models (Order, CreateOrderRequest) and service functions (create_order, list_orders) that keep orders in memory.
• mcp_server/ — MCP server built with FastMCP: exposes two tools that call into app.
• mcp.json — Example MCP config for Cursor (or copy into .cursor/mcp.json or ~/.cursor/mcp.json).

How MCP fits in

1. MCP server = process that exposes tools (and optionally resources, prompts). Here it’s mcp_server/server.py, which runs over stdio and talks JSON-RPC.
2. MCP client = app that discovers and calls those tools. Cursor is an MCP client; when you add this server in Cursor’s MCP settings, Cursor spawns the server and sends tool calls to it.
3. Tools = named functions with typed arguments. This server exposes:
   • create_order_tool(product_id, quantity) — creates an order and returns it.
   • list_orders_tool() — returns all orders.

So “how MCP works” here: Cursor sends a tool call (e.g. create order with product_id 1, quantity 255) → MCP server receives it → server calls create_order → returns the new order as the tool result → Cursor shows it to you.

Setup

cd /path/to/MCP
python -m venv venv
source venv/bin/activate   # or `venv\Scripts\activate` on Windows
pip install -r requirements.txt

Run the MCP server locally (stdio)

From the project root:

python mcp_server/server.py

The server runs over stdio and waits for JSON-RPC messages. It will exit quickly if nothing is connected; that’s expected. To use it, run it via an MCP client (e.g. Cursor).

Use with Cursor

1. Config — Cursor reads MCP config from:

   • Project: .cursor/mcp.json
   • User: ~/.cursor/mcp.json

2. Example config (adjust paths if needed):

   {
     "mcpServers": {
       "orders-server": {
         "command": "/path/to/MCP/venv/bin/python",
         "args": ["mcp_server/server.py"],
         "cwd": "/path/to/MCP"
       }
     }
   }
   

   cwd must be the project root so the app package can be imported.

3. Restart Cursor (or reload MCP) so it picks up the config and starts the server.

4. In Cursor you can then call the create order and list orders tools (e.g. from the MCP / Composer tools UI).

Project layout

MCP/
├── app/
│   ├── schema.py      # Order, CreateOrderRequest (Pydantic)
│   ├── service.py     # create_order(), list_orders() — in-memory store
│   └── main.py        # optional FastAPI app (not required for MCP)
├── mcp_server/
│   └── server.py      # FastMCP server, create_order_tool, list_orders_tool
├── mcp.json           # example MCP config for Cursor
├── requirements.txt
└── README.md

Tech used

• Python 3
• MCP — Model Context Protocol SDK
• FastMCP — from the MCP package, for defining tools and running the stdio server
• Pydantic — request/response models

This repo is for learning: minimal persistence (in-memory only), no database, no auth — just enough to see how an MCP server exposes tools and how a client calls them.