501 Not Implemented

The HTTP 501 Not Implemented server error response status code means that the server does not support the functionality required to fulfill the request.

A response with this status may also include a Retry-After header, telling the client that they can retry the request after the specified time has elapsed. A 501 response is cacheable by default unless caching headers instruct otherwise.

501 is the appropriate response when the server does not recognize the request method and is incapable of supporting it for any resource. Servers are required to support GET and HEAD, and therefore must not return 501 in response to requests with these methods. If the server does recognize the method, but intentionally does not allow it, the appropriate response is 405 Method Not Allowed.

If you have visited a web page and you are seeing 501 errors, these issues require investigation and fixing by server owners or administrators. You can clear your browser cache for the domain, disable proxies if you are using one, or try again later to see if it works as expected.

A 501 response can occur if proxies cannot not handle request methods used in the context of HTTP Extension Framework (RFC 2774) applications. This status can also occur in Web Distributed Authoring and Versioning (WebDAV) when a request method (SEARCH, PROPFIND) does not have a URL handler configured to process it.

501 Not Implemented

M-GET /document HTTP/1.1
Host: example.com
C-Man: "http://www.example.org/"
Connection: C-Man

HTTP/1.1 501 Not Implemented