501 Not Implemented

Takeaways

Note

A 501 error is not something you can fix, but requires a fix by the web server you are trying to access.

1. The server does not support the functionality required to fulfil the request.
2. This is the appropriate response when the server does not recognize the request method and is not capable of supporting it for any resource.
3. A 501 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls.

Information

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

This status can also send a Retry-After header, telling the requester when to check back to see if the functionality is supported by then.

501 is the appropriate response when the server does not recognize the request method and is incapable of supporting it for any resource. The only methods that servers are required to support (and therefore that must not return 501) are GET and HEAD.

If the server does recognize the method, but intentionally does not support it, the appropriate response is 405 Method Not Allowed.

A 501 response is cacheable by default; that is, unless caching headers instruct otherwise.