HTTP 501 Not Implemented vs 506 Variant Also Negotiates
Both HTTP 501 (Not Implemented) and 506 (Variant Also Negotiates) belong to the 5xx Server Error category. 501 indicates that the server does not support the functionality required to fulfill the request. The server either does not recognize the request method or lacks the ability to fulfill it. Meanwhile, 506 means that the server has an internal configuration error: the chosen variant resource is configured to engage in content negotiation itself.
Description
The server does not support the functionality required to fulfill the request. The server either does not recognize the request method or lacks the ability to fulfill it.
When You See It
When using an HTTP method (like PATCH) that the server doesn't support.
How to Fix
Use a different HTTP method that the server supports. Check server documentation.
Description
The server has an internal configuration error: the chosen variant resource is configured to engage in content negotiation itself.
When You See It
Rare. Indicates a misconfigured server-side content negotiation loop.
How to Fix
Fix the server's content negotiation configuration.
Key Differences
HTTP 501: The server does not support the functionality required to fulfill the request. The server either does not recognize the request method or lacks the ability to fulfill it.
HTTP 506: The server has an internal configuration error: the chosen variant resource is configured to engage in content negotiation itself.
You encounter 501 when when using an HTTP method (like PATCH) that the server doesn't support.
You encounter 506 when rare. Indicates a misconfigured server-side content negotiation loop.
When to Use Which
For 501 (Not Implemented): Use a different HTTP method that the server supports. Check server documentation. For 506 (Variant Also Negotiates): Fix the server's content negotiation configuration.