httpstatuses/contents/codes/501.md

set	code	title	references
5	501	Not Implemented	Rails HTTP Status Symbol :not_implemented

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

This is the appropriate response when the server does not recognize the request method and is not capable of supporting it for any resource.

A 501 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls¹.

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• ¹ Calculating Heuristic Freshness RFC7234 Section 4.2.2
• Source: RFC7231 Section 6.6.2