How to Build an MCP Server in Python

An MCP server in Python exposes tools, resources, and prompts to AI hosts through the Model Context Protocol (MCP). You write a small Python program. Cursor, Claude Desktop, or another MCP host starts the program and calls your functions when the model needs live data.

This tutorial builds a local SQLite query server with the official MCP Python SDK and FastMCP. You register one tool, connect the server to Cursor and Claude Desktop, and confirm the model reads your database at chat time.

For protocol background, start with DigitalOcean’s MCP 101: An Introduction to Model Context Protocol and Understanding Model Context Protocol (MCP).

• An MCP server in Python uses the mcp package. Pin mcp>=1.27,<2 until the stable 2.x release ships.
• FastMCP (from mcp.server.fastmcp import FastMCP) registers tools with @mcp.tool() and runs over stdio by default for local hosts.
• MCP has three primitives: tools (model actions), resources (read-only data), and prompts (reusable templates). This tutorial focuses on tools.
• Local hosts start your server as a subprocess. Cursor reads ~/.cursor/mcp.json. Claude Desktop reads claude_desktop_config.json under both mcpServers keys.
• Use absolute paths to your virtualenv Python binary and server script in every config file.
• On stdio transports, log to stderr. Never print() to stdout or you break JSON-RPC messages.
• After setup, the host shows a green status dot (Cursor) or a tools icon (Claude Desktop). Approve each tool call before the server runs.

• Why MCP matters for LLM apps
• How to build a Python MCP server with FastMCP and SQLite
• How to register the server in Cursor and Claude Desktop
• How to test tool calls end to end
• Where to go next for remote MCP and production deployment

Before you start, confirm you have:

• Python 3.10 or newer (the official MCP Python quickstart requires 3.10+)
• pip and venv (bundled with current Python installers)
• Cursor with MCP enabled, or Claude Desktop for the second integration test
• A terminal on macOS or Linux, or PowerShell on Windows
• Network access to download the sample community.db file

MCP is an open protocol for connecting LLM hosts to external data and actions. Anthropic introduced MCP in November 2024. Hosts speak JSON-RPC over stdio or HTTP transports. Servers expose structured capabilities instead of custom one-off integrations per model.

Large language models predict text. They do not query your database or call your APIs unless a host routes a tool call to a server you control. MCP standardizes that bridge.

When you chat in Cursor or Claude Desktop, the host is the app window. The MCP client inside the host lists available tools, sends your message to the model, and forwards approved tool calls to your server.

1. You ask a question, for example “List the top chatters.”
2. The model selects the get_top_chatters tool if the description matches.
3. The host asks you to approve the tool call.
4. The MCP client sends the call to your Python server over stdio.
5. The server queries SQLite and returns JSON rows.
6. The model formats the answer in the chat.

Everything in the diagram runs on your machine for this walkthrough. The host spawns your server locally. The server opens community.db on disk.

This project implements one tool. Resources and prompts follow the same FastMCP decorators (@mcp.resource(), @mcp.prompt()). See the MCP Python SDK server docs for full examples.

You will create a virtual environment, install the SDK, download sample data, and write sqlite-server.py.

Step 1: Set up your environment

Create and activate a virtual environment:

python3 -m venv mcp-env
source mcp-env/bin/activate

On Windows PowerShell:

python -m venv mcp-env
mcp-env\Scripts\Activate.ps1

Install the MCP Python SDK. Pin below 2.x while v2 is in alpha:

pip install "mcp>=1.27,<2"

Step 2: Download the sample database

Download community.db into the same folder as your server script. The file contains a chatters table with name and messages columns.

For SQLite fundamentals in a web app context, see How To Use an SQLite Database in a Flask Application.

Step 3: Write the MCP server

Create sqlite-server.py:

# sqlite-server.py
from pathlib import Path

import sqlite3
from mcp.server.fastmcp import FastMCP

DB_PATH = Path(__file__).resolve().parent / "community.db"

mcp = FastMCP("Community Chatters")


@mcp.tool()
def get_top_chatters(limit: int = 10) -> list[dict]:
    """Return chatters ranked by message count."""
    conn = sqlite3.connect(DB_PATH)
    cursor = conn.cursor()
    cursor.execute(
        "SELECT name, messages FROM chatters ORDER BY messages DESC LIMIT ?",
        (limit,),
    )
    rows = cursor.fetchall()
    conn.close()
    return [{"name": name, "messages": messages} for name, messages in rows]


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

FastMCP reads the function name, type hints, and docstring to build the tool schema. mcp.run() starts the stdio transport, which local hosts expect.

Test the query without the host:

python3 -c "import sqlite3; c=sqlite3.connect('community.db'); print(c.execute('SELECT COUNT(*) FROM chatters').fetchone())"

You should see a row count printed to the terminal.

Open Cursor → Settings → MCP and click Add a New Global MCP Server. Cursor opens ~/.cursor/mcp.json.

Replace the placeholder paths with your absolute paths. Run which python inside your activated virtualenv to get the interpreter path.

{
  "mcpServers": {
    "sqlite-server": {
      "command": "/absolute/path/to/mcp-env/bin/python",
      "args": [
        "/absolute/path/to/sqlite-server.py"
      ],
      "description": "Query top chatters from the community SQLite database"
    }
  }
}

Save the file and return to MCP Settings. A green dot next to the server name means the process started cleanly.

1. Open a chat and ask: “How many chatters are in the database?”
2. Cursor proposes the get_top_chatters tool. Approve the prompt.
3. The server returns rows. The model summarizes them in the reply.

If the tool never appears, see Troubleshooting below.

Claude Desktop uses the same mcpServers object shape as Cursor.

1. Open Claude Desktop → Settings → Developer → Edit Config.
2. Edit claude_desktop_config.json (macOS: ~/Library/Application Support/Claude/claude_desktop_config.json).
3. Add your server block with the same command and args paths as Cursor.
4. Save, quit Claude Desktop completely, and reopen the app.

{
  "mcpServers": {
    "sqlite-server": {
      "command": "/absolute/path/to/mcp-env/bin/python",
      "args": [
        "/absolute/path/to/sqlite-server.py"
      ]
    }
  }
}

Ask Claude: “Show me the top five chatters.” Approve the tool call when prompted.

The same Python server now works from two hosts. The model brand changes. The MCP contract stays the same.

Claude Desktop writes MCP logs to ~/Library/Logs/Claude/mcp*.log on macOS. See Connect to local MCP servers for log locations on other platforms.

1. What is MCP in Python?

MCP in Python means you implement a Model Context Protocol server with the mcp package (FastMCP on top). The server exposes tools the host forwards to the model. Python is one supported language. The TypeScript SDK serves the same role for Node hosts.

2. What is the best Python MCP library for building a server?

You can use the official mcp package with FastMCP from mcp.server.fastmcp. Install with pip install "mcp>=1.27,<2". The standalone fastmcp project targets the same ergonomic API for HTTP-first deployments. Start with the official SDK so your code matches modelcontextprotocol.io docs.

3. How do you create an MCP server in Python?

1. Create a virtualenv and pip install "mcp>=1.27,<2".
2. Instantiate FastMCP("ServerName").
3. Register functions with @mcp.tool().
4. Call mcp.run() under if __name__ == "__main__":.
5. Point Cursor or Claude Desktop at the venv Python and your script path in mcpServers.

The create-python-server scaffold generates a starter repo if you prefer a template.

4. What is the difference between an MCP SDK and MCP?

MCP is the protocol specification (messages, transports, capability types). An MCP SDK is a language library that implements the spec. The Python SDK handles JSON-RPC framing, schema generation, and stdio or HTTP transports so you focus on tool logic.

5. Is MCP just a REST API?

No. MCP uses JSON-RPC messages and a defined capability model (tools, resources, prompts). Hosts spawn stdio servers or connect over Streamable HTTP. REST endpoints are optional. You wrap existing REST APIs inside tool functions, but the wire format is not plain HTTP CRUD.

You built an MCP server in Python with FastMCP, wired SQLite data into Cursor and Claude Desktop, and validated tool calls end to end. The same pattern extends to email gateways, cloud APIs, and deployment workflows.

Grow from this local stdio server into production-oriented patterns:

• From Prompt to App in Minutes with the DigitalOcean MCP Server for App Platform actions from Claude or Cursor
• How to Use MCP with OpenAI Agents for agent frameworks beyond desktop hosts
• Claude Code MCP Server for terminal-based agent workflows
• MongoDB and DigitalOcean MCP Server Tutorial for database-backed MCP at scale
• MCP Python SDK on GitHub for resources, prompts, and Streamable HTTP examples

Run experiments on a DigitalOcean Droplet or ship apps with App Platform. For managed models and knowledge bases, explore the DigitalOcean AI Platform.