What it means
The server does not support the functionality required, typically the request method itself.
Common causes
- Unknown or unsupported method such as PATCH on an old server
- A feature that is not implemented yet
How to fix it
As a client or visitor
Use a supported method or endpoint.
As the site or API owner
Return 405 if the method is known but not allowed for that resource; 501 is for methods the server does not recognize at all.
Example response
HTTP/1.1
HTTP/1.1 501 Not Implemented
Date: Tue, 07 Oct 2025 09:30:00 GMT
Server: nginx
Content-Length: 0Specification
FAQ
› 501 vs 405?
405: this resource does not allow the method. 501: the server does not implement the method anywhere.
› Is 501 cacheable?
Yes, by default, unless headers say otherwise.