Fix MCP tool not found error
tool not found error in MCP occurs when the MCP Python SDK is not installed or the tool is not properly registered. Ensure you have installed the mcp package via pip and import stdio_server from mcp.server.stdio to run the MCP server correctly.config_error mcp package with pip install mcp and import stdio_server from mcp.server.stdio to fix the tool not found error.Why this happens
The tool not found error typically occurs when the MCP Python SDK is not installed or the MCP server is not properly initialized with the correct tool registration. For example, running code that imports mcp.server without installing the mcp package or trying to start the server without specifying the stdio_server transport triggers this error.
Typical error output:
ModuleNotFoundError: No module named 'mcp' OR RuntimeError: MCP tool not found or not registered
import mcp.server
server = mcp.server.Server()
server.serve()ModuleNotFoundError: No module named 'mcp'
The fix
Install the official MCP Python SDK using pip install mcp. Then, import stdio_server from mcp.server.stdio and run it to start the MCP server correctly. This ensures the MCP tool is registered and available.
This works because stdio_server is the recommended entry point for MCP servers using standard input/output transport, which automatically registers the tool and handles communication.
from mcp.server.stdio import stdio_server
if __name__ == "__main__":
stdio_server()MCP server started on stdio transport
Preventing it in production
Always verify the mcp package is installed in your deployment environment. Use virtual environments to isolate dependencies. Add startup checks to confirm the MCP server starts without errors. Implement retry logic or fallback mechanisms if the MCP tool fails to initialize. Monitor logs for tool not found errors to catch configuration issues early.
Key Takeaways
- Install the MCP Python SDK with `pip install mcp` before running MCP servers.
- Use `stdio_server` from `mcp.server.stdio` to properly register and start the MCP tool.
- Validate MCP server startup in production to avoid tool not found errors.
- Monitor logs and implement retries for robust MCP tool initialization.