HTTP 501 Not Implemented — Meaning, Causes & How to Fix

Code

501

Name

Not Implemented

Class

5xx Server Error

Specification

RFC 9110 §15.6.2

Cacheable by default

Yes — heuristically cacheable by default

What HTTP 501 means

501 Not Implemented means the server does not support the functionality needed — usually it does not recognise the request method at all for any resource. It is one of the few 5xx codes that is heuristically cacheable.

Common causes

• A client using an unusual method (e.g. PROPFIND or a custom verb) on a server that does not support it.
• An API placeholder endpoint that is not built yet.

How to fix it

For site owners

• If the method should work, enable the module or handler for it.
• Use 405 instead if the method is supported elsewhere but not on this URL.

For visitors & developers

• Use a standard method (GET, POST, PUT, DELETE…) supported by the server.

SEO impact

Rare for pages, as crawlers use GET. Any 5xx returned to GET requests slows crawling and can drop URLs if it persists.

Example 501 response

HTTP/1.1 501 Not Implemented
Content-Type: text/plain

Method PROPFIND is not supported.

Related status codes

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