MCP server not showing tools fix
Quick answer
To fix
MCP server not showing tools, ensure you properly register your tools with the Server instance before starting it. Also, use the stdio_server transport or another supported transport to enable tool visibility and communication.PREREQUISITES
Python 3.8+pip install mcpBasic knowledge of Python async programming
Setup MCP environment
Install the mcp Python package and prepare your environment variables if needed. MCP requires Python 3.8 or higher.
pip install mcpStep by step MCP server with tools
Register your tools explicitly with the Server instance and start the server using the stdio_server transport to ensure tools are visible and accessible.
import asyncio
from mcp.server import Server
from mcp.server.stdio import stdio_server
# Define a simple tool
async def echo_tool(input_text: str) -> str:
return f"Echo: {input_text}"
async def main():
# Create MCP server instance
server = Server()
# Register tools explicitly
server.register_tool("echo", echo_tool)
# Start the server with stdio transport
await stdio_server(server)
if __name__ == "__main__":
asyncio.run(main())Common variations
- Use different transports like SSE or TCP if stdio is not suitable.
- Register multiple tools by calling
server.register_tool()multiple times. - Use synchronous tools by wrapping them with
asyncio.to_threadif needed.
import asyncio
from mcp.server import Server
from mcp.server.stdio import stdio_server
# Synchronous tool example
def sync_tool(data: str) -> str:
return data.upper()
async def main():
server = Server()
# Wrap sync tool for async
async def async_sync_tool(data: str) -> str:
return await asyncio.to_thread(sync_tool, data)
server.register_tool("uppercase", async_sync_tool)
await stdio_server(server)
if __name__ == "__main__":
asyncio.run(main())Troubleshooting
- If tools do not appear, verify you called
server.register_tool()before starting the server. - Ensure you use the correct transport like
stdio_serverwhich supports tool communication. - Check for exceptions during tool registration or server start; unhandled exceptions can prevent tools from showing.
- Confirm your client or agent supports MCP and is connected properly to the server.
Key Takeaways
- Always register tools with
server.register_tool()before starting the MCP server. - Use
stdio_serveror a supported transport to enable tool visibility and communication. - Wrap synchronous tools with
asyncio.to_threadfor async compatibility. - Check for exceptions during server startup to avoid silent failures hiding tools.
- Verify client compatibility and connection to the MCP server for proper tool listing.