HTTP 304 Not Modified vs 510 Not Extended
HTTP 304 (Not Modified) is a 3xx Redirection response, while 510 (Not Extended) is a 5xx Server Error response. 304 indicates that the resource has not been modified since the last request. The client can use its cached copy. In contrast, 510 means that further extensions to the request are required for the server to fulfill it.
Description
The resource has not been modified since the last request. The client can use its cached copy.
When You See It
When the browser cache is still valid (If-None-Match / If-Modified-Since headers match).
How to Fix
No fix needed. This saves bandwidth by confirming the cached version is still current.
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
304 is a 3xx Redirection response, while 510 is a 5xx Server Error response.
HTTP 304: The resource has not been modified since the last request. The client can use its cached copy.
HTTP 510: Further extensions to the request are required for the server to fulfill it.
You encounter 304 when when the browser cache is still valid (If-None-Match / If-Modified-Since headers match).
You encounter 510 when when an HTTP extension required by the server is not present in the request.
When to Use Which
For 304 (Not Modified): No fix needed. This saves bandwidth by confirming the cached version is still current. For 510 (Not Extended): Add the required extension headers to your request.