stdio servers that wait on a prompt, a GUI login, or DNS will look like a timeout in the client. Run the same command in a terminal.
Remote HTTP endpoints hang on expired OAuth, a corporate proxy, or a tool that is still paging. Bound the call and retry once.
Do not stack retries on a write. If list_dir never returns, kill the process from the client and fix PATH or the allow list.
See debug-MCP-connection and transports. A hung server still holds whatever files or tokens it already opened.