Front desk · HTTP Status Codes
5×× Server Error
501 Not Implemented
· filed 2026-07-18 · click a code to copy
HTTP 501 Not Implemented is a server error-class status code defined in RFC9110. The server does not support the functionality required to fulfil the request.
Server-error responses admit the fault is on the server's side: the request was valid, but the server failed to fulfil it. On the wire, the response begins with the status line HTTP/1.1 501 Not Implemented.