MCP Server Standard - FastMCP

All Nexus 3.0 MCP servers use FastMCP, the official Anthropic MCP library. This ensures protocol compliance, reduces boilerplate, and enables future updates through library upgrades.

Why FastMCP

Server Structure

#!/usr/bin/env python3
"""Nexus {Environment} MCP Server v1.0.0"""

import json
import redis
from mcp.server.fastmcp import FastMCP

# Import credentials helper
import sys
sys.path.insert(0, '/opt/mcp-servers/shared')
from credentials_helper import get_environment_config

# Initialize FastMCP
mcp = FastMCP("{environment}")

# Get credentials from Locker
config = get_environment_config('{environment}')
ENV_CONFIG = {
    'vault_port': config.get('vault_port'),
    'operational_port': config.get('operational_port'),
    'vault_password': config.get('vault_password'),
}

# Manager class for business logic
class EnvironmentManager:
    def __init__(self):
        self.vault = redis.Redis(
            host='localhost',
            port=ENV_CONFIG['vault_port'],
            password=ENV_CONFIG['vault_password'],
            decode_responses=True
        )
        # Operational has no password (read-only slave)
        self.operational = redis.Redis(
            host='localhost',
            port=ENV_CONFIG['operational_port'],
            decode_responses=True
        )

manager = EnvironmentManager()

# Define tools with decorators
@mcp.tool()
async def status() -> str:
    """Get environment status."""
    # YOUR BUSINESS LOGIC HERE
    return json.dumps({'status': 'UP'})

@mcp.tool()
async def create(name: str, data: str = None) -> str:
    """Create a new item.

    Args:
        name: Item name (required)
        data: Optional data payload
    """
    # YOUR BUSINESS LOGIC HERE
    return json.dumps({'created': name})

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

Key Points

1. FastMCP Import

from mcp.server.fastmcp import FastMCP
mcp = FastMCP("{server_name}")

2. Tool Decorators

@mcp.tool()
async def tool_name(param: str, optional: str = None) -> str:
    """Tool description - first line becomes the tool summary.

    Args:
        param: Description of required param
        optional: Description of optional param
    """
    return json.dumps(result)

3. Main Entry Point

if __name__ == "__main__":
    mcp.run()  # FastMCP handles all protocol

Gateway Compatibility

The Gateway server (/opt/mcp-servers/gateway/mcp_gateway_server.py) sends proper MCP protocol handshakes:

1. initialize with protocolVersion, capabilities, clientInfo
2. notifications/initialized notification
3. tools/call with tool name and arguments

This is required for FastMCP compliance.

Migration from Raw MCP

When converting existing servers:

1. Replace custom class with FastMCP instance
2. Convert methods to @mcp.tool() decorated async functions
3. Remove manual JSON-RPC handling (~60 lines)
4. Keep all business logic unchanged
5. Replace if __name__ == "__main__": with mcp.run()

File Location

All MCP servers live at:

/opt/mcp-servers/{environment}/mcp_{environment}_server.py

Dependencies

pip install mcp redis

The mcp package includes FastMCP and is maintained by Anthropic.