HTTP 412 Precondition Failed vs 510 Not Extended
HTTP 412 (Precondition Failed) is a 4xx Client Error response, while 510 (Not Extended) is a 5xx Server Error response. 412 indicates that one or more conditions in the request headers (If-Match, If-Unmodified-Since) evaluated to false. In contrast, 510 means that further extensions to the request are required for the server to fulfill it.
Description
One or more conditions in the request headers (If-Match, If-Unmodified-Since) evaluated to false.
When You See It
When using conditional requests with ETags and the resource has changed.
How to Fix
Refresh the ETag/Last-Modified value and retry with updated preconditions.
Description
Further extensions to the request are required for the server to fulfill it.
When You See It
When an HTTP extension required by the server is not present in the request.
How to Fix
Add the required extension headers to your request.
Key Differences
412 is a 4xx Client Error response, while 510 is a 5xx Server Error response.
HTTP 412: One or more conditions in the request headers (If-Match, If-Unmodified-Since) evaluated to false.
HTTP 510: Further extensions to the request are required for the server to fulfill it.
You encounter 412 when when using conditional requests with ETags and the resource has changed.
You encounter 510 when when an HTTP extension required by the server is not present in the request.
When to Use Which
For 412 (Precondition Failed): Refresh the ETag/Last-Modified value and retry with updated preconditions. For 510 (Not Extended): Add the required extension headers to your request.