501 Not Implemented

We never built that.

What it properly means

The server does not support the request method. Only GET and HEAD are required, so those must never return this.

Class
5xx Server error: we fucked up
Defined in
RFC 9110, section 15.6.2

Get one yourself

This endpoint really answers with 501. Point your client at it and see what it does.

curl -i https://httpcodes.dev/api/501

People mix this up with

  • 405 Method Not Allowed501

    Not allowed here, or not built at all?

    405 means the server understands the method but this resource does not take it. 501 means the server does not support that method anywhere.