Are logging and progress notifications required in MCP?

No, implementing these notifications is entirely optional on both the server and client sides. A server can run tools without ever sending a log message or progress update, and a client can choose to ignore any notifications it receives. They are purely user experience enhancements designed to help users understand what is happening during long-running operations. However, for tools that take more than a few seconds, adding notifications dramatically improves perceived reliability because users can see that work is actually happening.