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MCP Simple Server

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from oleksandrsirenko

A simple MCP server with streamable HTTP transport that supports basic math tools like add and multiply.

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MCP Simple Server

A minimal, reference implementation of a Model Context Protocol server with streamable HTTP transport. Built with FastMCP following the official Anthropic MCP specification 2025-06-18. Perfect starting point for building remote MCP servers.

🎯 Purpose

This project serves as a simple, well-documented reference for developers who want to:

  • Build their first MCP server
  • Deploy MCP servers to cloud platforms (Railway, Heroku, Render)
  • Understand the MCP protocol implementation
  • Create a foundation for more sophisticated MCP solutions

Features

  • ✅ Two Math Tools: add and multiply functions
  • ✅ Streamable HTTP Transport: Modern MCP protocol with SSE support
  • ✅ Session Management: Proper MCP initialization flow
  • ✅ Remote Deployment: Railway, Heroku, Render deployment configs
  • ✅ Automated Testing: Complete protocol validation and debugging tools
  • ✅ Claude Desktop Integration: Ready for AI assistant integration
  • ✅ Reference Implementation: Well-documented code for learning

Available Tools

add(a, b)

Adds two numbers together.

Example:

{"name": "add", "arguments": {"a": 25, "b": 17}}
→ Returns: 42

multiply(a, b)

Multiplies two numbers together.

Example:

{"name": "multiply", "arguments": {"a": 8, "b": 6}}
→ Returns: 48

Manual Testing with curl

Local Testing (Development)

For testing your local development server running on localhost:8000:

1. Initialize Session

curl -X POST http://localhost:8000/mcp/ \
  -H "Content-Type: application/json" \
  -H "MCP-Protocol-Version: 2025-06-18" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{"tools":{}},"clientInfo":{"name":"test-client","version":"1.0.0"}}}'

2. Send Initialized Notification

curl -X POST http://localhost:8000/mcp/ \
  -H "Content-Type: application/json" \
  -H "MCP-Protocol-Version: 2025-06-18" \
  -H "Accept: application/json, text/event-stream" \
  -H "Mcp-Session-Id: YOUR_SESSION_ID" \
  -d '{"jsonrpc":"2.0","method":"notifications/initialized"}'

3. List Tools

curl -X POST http://localhost:8000/mcp/ \
  -H "Content-Type: application/json" \
  -H "MCP-Protocol-Version: 2025-06-18" \
  -H "Accept: application/json, text/event-stream" \
  -H "Mcp-Session-Id: YOUR_SESSION_ID" \
  -d '{"jsonrpc":"2.0","id":2,"method":"tools/list"}'

4. Call Add Tool

curl -X POST http://localhost:8000/mcp/ \
  -H "Content-Type: application/json" \
  -H "MCP-Protocol-Version: 2025-06-18" \
  -H "Accept: application/json, text/event-stream" \
  -H "Mcp-Session-Id: YOUR_SESSION_ID" \
  -d '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"add","arguments":{"a":25,"b":17}}}'

Remote Testing (Production)

For testing your deployed server, replace localhost:8000 with your deployment URL:

# Example with Railway deployment
curl -X POST https://your-app.railway.app/mcp/ \
  -H "Content-Type: application/json" \
  -H "MCP-Protocol-Version: 2025-06-18" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{"tools":{}},"clientInfo":{"name":"test-client","version":"1.0.0"}}}'

Note: For comprehensive remote testing, use the automated test script:

python test_deployment.py your-app.railway.app

Claude Desktop Integration

Local Server Configuration

{
  "mcpServers": {
    "simple-server": {
      "command": "python",
      "args": ["main.py"],
      "cwd": "/path/to/mcp-simple-server"
    }
  }
}

For remote servers deployed to Railway, Heroku, or Render, use the mcp-remote package:

{
  "mcpServers": {
    "simple-server-remote": {
      "command": "npx",
      "args": [
        "-y",
        "mcp-remote",
        "https://your-app.railway.app/mcp/",
        "--allow-http",
        "--header",
        "Accept: application/json, text/event-stream"
      ]
    }
  }
}

Key Configuration Notes:

  • Use npx with the -y flag to auto-install mcp-remote
  • Include the trailing slash in the URL: /mcp/
  • Add the --allow-http flag for HTTP connections
  • Include the Accept header for proper SSE support

Alternative: Direct Python Proxy (Advanced)

For advanced users or debugging purposes, you can create a custom Python proxy:

{
  "mcpServers": {
    "simple-server-proxy": {
      "command": "python",
      "args": ["claude_mcp_proxy.py"],
      "cwd": "/path/to/mcp-simple-server"
    }
  }
}

Note: This requires the claude_mcp_proxy.py script from the repository and is mainly for debugging purposes. Use mcp-remote for production.

Configuration File Locations:

  • macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
  • Windows: %APPDATA%\Claude\claude_desktop_config.json

Test with Claude

After integration, ask Claude:

  • "Can you add 42 and 18 for me?"
  • "What's 7 times 9?"
  • "What tools do you have available?"

Claude will use your MCP server to perform calculations! 🎉

Development

Adding New Tools

@mcp.tool()
def subtract(a: float, b: float) -> float:
    """Subtract two numbers"""
    return a - b

@mcp.tool()
def divide(a: float, b: float) -> float:
    """Divide two numbers"""
    if b == 0:
        raise ValueError("Cannot divide by zero")
    return a / b

Environment Variables

  • HOST: Server host (default: 127.0.0.1, use 0.0.0.0 for deployment)
  • PORT: Server port (default: 8000, Railway sets this automatically)
HOST=0.0.0.0 PORT=3000 python main.py

Note: For Railway deployment, FastMCP will automatically bind to 0.0.0.0:$PORT.

Project Structure

mcp-simple-server/
├── main.py                    # MCP server (~25 lines)
├── test_server.py             # Local server tests (~300 lines)
├── test_deployment.py         # Remote deployment tests
├── test_host_binding.py       # Host binding tests
├── test_proxy_script.py       # Proxy testing script
├── test_streamable_app.py     # Streamable HTTP tests
├── test_tool_verification.py  # Tool verification tests
├── debug_railway_server.py    # Railway debugging utilities
├── debug_fastmcp.py           # FastMCP debugging utilities
├── claude_mcp_proxy.py        # Claude Desktop proxy (optional)
├── start.sh                   # Shell startup script
├── pyproject.toml             # Project configuration
├── README.md                  # This documentation
├── uv.lock                    # Dependency lock file
├── .gitignore                 # Git ignore patterns
├── .python-version            # Python version specification
├── Dockerfile                 # Docker deployment
├── railway.toml               # Railway configuration
├── Procfile                   # Heroku configuration
└── render.yaml                # Render configuration

Architecture

  • FastMCP: High-level MCP implementation from Anthropic
  • Streamable HTTP: Modern transport with SSE streaming support
  • Session Management: Stateful connections with session IDs
  • JSON-RPC 2.0: Standard protocol for message exchange
  • Protocol 2025-06-18: Latest MCP specification
  • Port 8000: Default FastMCP server port (configurable via PORT env var)

Technical Details

Server Implementation

  • Framework: FastMCP (official Anthropic library)
  • Transport: Streamable HTTP with Server-Sent Events
  • Protocol: MCP 2025-06-18 specification
  • Dependencies: httpx>=0.28.1, mcp>=1.9.4

MCP Protocol Flow

  1. Client sends initialize request
  2. Server responds with capabilities and session ID
  3. Client sends initialized notification
  4. Normal operations begin (tools/list, tools/call, etc.)

Tool Response Format

Tools return simple Python values (float, int, str) which FastMCP automatically wraps in the proper MCP response format.

Dependencies

dependencies = [
    "httpx>=0.28.1",   # HTTP client for testing
    "mcp>=1.9.4",      # Official Anthropic MCP library
]

The project uses:

  • mcp: Official Anthropic MCP Python SDK
  • httpx: Modern HTTP client for automated testing
  • Python: Requires Python >=3.10

Resources