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Existing OpenAPI to an MCP Server Using FastMCP

2 min readAIMCPGen AiModel Context Protocol

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In this brief tutorial, we’ll use FastMCP to transform an existing TODO application (which exposes an OpenAPI spec) into a MCP server and link it to CoPilot for organic task interactions.

Step 1: The TODO App #

Your TODO app should already be running at:

http://localhost:8000

And exposing its OpenAPI spec at:

http://localhost:8000/openapi.json

Step 2: Create the MCP Server #

Create a file todo_mcp_server.py:

import httpx
from fastmcp import FastMCP

client = httpx.AsyncClient(base_url="http://localhost:8000")
spec = httpx.get("http://localhost:8000/openapi.json").json()
mcp = FastMCP.from_openapi(openapi_spec=spec, client=client)

if __name__ == "__main__":
    mcp.run(
        transport="http",
        host="localhost",
        port=4200,
        path="/todo-mcp/http",
        log_level="debug",
    )

Run it:

python todo_mcp_server.py

Your MCP server will be available at:

http://localhost:4200/todo-mcp/http

Step 3: Add to CoPilot #

In your mcp.json:

{
  "servers": {
    "todo": {
      "url": "http://localhost:4200/todo-mcp/http"
    }
  }
}

Step 4: Sample Conversations #

You: list all the tasks

CoPilot:

Here is the list of all tasks:

1. Review project proposal - Review and provide feedback on the Q1 project proposal  
   (Priority: High, Category: Work)

2. Buy groceries - Milk, eggs, bread, and vegetables  
   (Priority: Medium, Category: Personal)

3. Call dentist - Schedule annual checkup  
   (Priority: Low, Category: Health)

You: add a new task to buy laptop next monday

CoPilot:

Task "Buy laptop" added with due date August 11, 2025.

You: list again

CoPilot:

Here is the list of all tasks:

1. Review project proposal - Review and provide feedback on the Q1 project proposal  
   (Priority: High, Category: Work)

2. Buy groceries - Milk, eggs, bread, and vegetables  
   (Priority: Medium, Category: Personal)

3. Call dentist - Schedule annual checkup  
   (Priority: Low, Category: Health)

4. Buy laptop - Purchase a new laptop  
   (Priority: Medium, Category: Personal, Due Date: August 11, 2025)

Let me know if you'd like to update, delete, or add any tasks!

That’s it! Your OpenAPI-based TODO app is now AI-ready with MCP + CoPilot.

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