Creating a Python MCP Server: A Step-by-Step Guide

The Model Context Protocol (MCP) provides a standardized approach for connecting context sources to large language models (LLMs). This tutorial demonstrates how to build a functional MCP server using Python's MCP SDK, enabling you to expose data, tools, and templates to LLM applications.

What is MCP?

MCP creates a bridge between LLM applications and external context sources. It allows you to modularize different aspects of LLM interactions:

• Data provision through resources (similar to read-only endpoints)

• Action execution via tools (comparable to API functions)

• Template management using prompts for reusable interactions

Related MCP server: MCP Server Demo

Core MCP Components

MCP servers implement three fundamental building blocks, each serving different purposes:

Understanding these distinctions helps you design effective MCP servers that properly separate concerns.

Server Feature Advertising

MCP servers announce their capabilities during startup, allowing clients to adapt their behavior:

Getting Started

Requirements

Ensure your environment includes:

• Python 3.7+ (Python 3.11+ recommended)

• pip package manager

• Node.js 18.x

Installation Options

Choose one of these installation methods:

Standard pip installation:

pip install "mcp[cli]"

Using uv (recommended for project management):

uv init mcp-server
cd mcp-server
uv add "mcp[cli]"

Project Structure

Organize your project as follows:

mcp-server/
├── server.py
├── pyproject.toml (if using uv)
└── README.md

Implementation

Building Your Server

Create server.py with the following foundation:

# server.py
from mcp.server.fastmcp import FastMCP

# Initialize the MCP server
mcp = FastMCP("Demo Server")

# Define a calculation tool
@mcp.tool()
def add(a: int, b: int) -> int:
    """
    Performs addition of two integers.
    
    Args:
        a: First number
        b: Second number
    
    Returns:
        Sum of both numbers
    """
    return a + b

# Create a dynamic resource
@mcp.resource("greeting://{name}")
def get_greeting(name: str) -> str:
    """
    Generates a personalized greeting.
    
    Args:
        name: Person's name for the greeting
    
    Returns:
        Formatted greeting message
    """
    return f"Hello, {name}!"

# Add a prompt template
@mcp.prompt()
def review_code(code: str) -> str:
    """
    Creates a code review template.
    
    Args:
        code: Source code to review
    
    Returns:
        Formatted review prompt
    """
    return f"Please review this code:\n\n{code}"

# Server execution
if __name__ == "__main__":
    mcp.run()

Testing Your Server

Using the Development Inspector

The most efficient way to test your server is through the built-in development interface:

mcp dev server.py

This command:

• Launches your server with live reloading

• Opens a web interface at http://localhost:6274/

• Provides interactive testing capabilities

Inspector Configuration

In the Inspector interface, configure the transport settings:

Transport Type: STDIO  
Command: python  
Arguments: server.py

Click Connect to establish the connection.

Testing Each Component

Tool Testing

1. Navigate to the Tools section

2. Select the add tool

3. Input test values (e.g., a = 10, b = 15)

4. Execute and verify the result (25)

Resource Testing

1. Go to Resources → Resource Templates

2. Select get_greeting

3. Enter a name (e.g., Alice)

4. Click Read Resource

5. Verify the response: "Hello, Alice!"

Prompt Testing

1. Access Prompts → List prompts

2. Select review_code

3. Input sample code: print(1+1)

4. Execute to see the formatted prompt output

Run this in a separate terminal while your server is active.

Understanding Server Behavior

When you run python server.py directly, the server appears inactive because it uses stdio transport and waits for client connections. This is normal behavior - the server needs a client (like the Inspector or your custom client) to interact with it.