3xx Redirection
304 Not Modified
The cached copy the client already holds is still fresh, so no body is sent.
What causes it
- The client sent `If-None-Match` with an ETag that still matches.
- The client sent `If-Modified-Since` and the resource has not changed.
How to fix it
- A 304 must not have a body, and must repeat the headers that would have been sent with a 200 (notably `ETag` and `Cache-Control`).
- Seeing stale content? Your ETag is probably not changing when the content does — hash the body, do not use the mtime of a rebuilt file.
At a glance
- Class
- 3xx Redirection
- Reference
- RFC 9110 §15.4.5
- Standardised
- Yes
- Retry the request?
- No — fix the request