Toronto SEO
All HTTP status codes
5xx Server Error
RFC 9110

501 Not Implemented

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

What it means

HTTP 501 Not Implemented means the server does not recognize the request method or lacks the ability to fulfill it. This is the appropriate response when the server does not recognize the method and is not capable of supporting it for any resource.

When it's used

Unsupported HTTP methods (e.g., PROPFIND on a non-WebDAV server), or features the server has not implemented yet.

Common causes
  • Client used PATCH on a server that only supports GET/POST
  • WebDAV method sent to a non-WebDAV server
  • Custom method not supported
How to fix it
  • Use a supported HTTP method
  • Implement the required method on the server
  • Check API documentation for supported methods
Example response
HTTP/1.1 501 Not Implemented
Allow: GET, POST
SEO impact

Should not affect crawlers (they only use GET and HEAD).