HTTP 501 Not Implemented

The server does not support the functionality required to fulfill the request.

Use 501 when the server genuinely does not implement the method or capability requested.

httpstatus codeserver errormethods

Response (http)

HTTP/1.1 501 Not Implemented

Use 501 when the server genuinely does not implement the method or capability requested.

Common mistakes

Using 500 for functionality the server never implemented; 501 tells clients the capability does not exist.

Registry reference: RFC9110, Section 15.6.2

Sources