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5xx Server error

501 Not Implemented

The server doesn't support the functionality needed for this request.

What 501 means

Usually the HTTP method itself isn't supported by the server at all (unlike 405, which is per endpoint).

Common causes

  • An unusual HTTP method (e.g. PATCH on an old server).
  • A feature planned but not built.

How to fix it

If you're calling an API

  • Use a supported method or endpoint.

If you run the server

  • Use 405 if the method is supported elsewhere.

Should you retry?

No.

Example response

HTTP
HTTP/1.1 501 Not Implemented
Content-Type: application/problem+json

{
  "type": "about:blank",
  "title": "Not Implemented",
  "status": 501,
  "detail": "The server doesn't support the functionality needed for this request."
}

Defined in: RFC 9110 (HTTP Semantics). 501 is a server error: the problem is on the server's side.

Debugging an API call? Convert your request with the cURL converter, check the response with the JSON formatter, or see whether the API is down on its status page.

HTTP 501 FAQ

What does HTTP 501 mean?

501 Not Implemented: The server doesn't support the functionality needed for this request. Usually the HTTP method itself isn't supported by the server at all (unlike 405, which is per endpoint).

Is 501 a client or server error?

It's a server error (5xx): the server failed to handle a valid request, so the fix is usually on the server's side.

How do I fix a 501 error?

Use a supported method or endpoint.

Should I retry after a 501?

No.

Other 5xx status codes

All HTTP status codes