501 Not Implemented

What is HTTP 501?

This status code indicates that the server does not support the HTTP method or feature needed to process the request. Unlike 405 Method Not Allowed, which means the method is recognized but not permitted for this resource, 501 means the server does not recognize or cannot implement the method at all. It is commonly returned for HTTP methods like TRACE, CONNECT, or custom methods that the server has not implemented.

Defined in RFC 9110

Common Causes

• Using an HTTP method that the server software does not recognize or support at all
• Sending a request that requires a protocol feature the server has not implemented
• A server that only supports GET and POST receiving a PATCH or OPTIONS request

How to Fix

• Use a different, supported HTTP method to achieve the same result
• Check the server documentation for which methods and features are supported
• If you control the server, implement the missing method handler
• Verify that your request uses a standard HTTP method and is properly formatted