HTTP 501 Not Implemented

Status code 501 · Class 5xx

HTTP

Not Implemented

Also searched as: error 501, HTTP 501, 501 not implemented

HTTP request chain from browser through CDN and proxy to the origin server
HTTP errors: find which hop in the request chain failed and read its logs.

What it means

The server does not support the functionality needed to fulfil the request, typically an HTTP method it does not recognise at all. It is a server-side capability gap rather than a temporary failure.

Applies to: REST APIs, nginx, Apache, IIS

How to fix HTTP 501 Not Implemented

  1. Retry with a standard method (GET or POST) if your client uses an unusual one
  2. Check whether a proxy or older server sits in front of the application and does not understand the method
  3. API clients: confirm the endpoint and method in the documentation
  4. If you own the site: implement the method in the application or route it to a component that supports it
  5. If you own the site: check proxy/WAF settings that reject methods such as PATCH or PROPFIND

Why it happens

Per RFC 9110, 501 means the server does not recognise the request method or lacks the ability to fulfil it for any resource. 405 is used instead when the method is known but not allowed on a specific URL.

FAQ

What is the difference between 501 and 405?

501 means the server does not support the method at all. 405 means it supports it elsewhere but not for this resource.

Related errors

ERR_EMPTY_RESPONSEHTTP 500 Internal Server ErrorHTTP 502 Bad GatewayHTTP 503 Service UnavailableHTTP 431 Request Header Fields Too LargeHTTP 504 Gateway TimeoutHTTP 301 Moved PermanentlyHTTP 302 Found

Source: IANA HTTP Status Code Registry · fixes written and reviewed by the editors (see our editorial policy)

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