304 3xx RFC 9110 §15.4.5

Not Modified

Cached resource is still valid. Client should use cached copy.

What HTTP 304 means

RFC 9110 §15.4.5. Returned in response to conditional GET (If-Modified-Since, If-None-Match). Body must be empty. Critical for HTTP caching efficiency.

Typical causes

Conditional GET with valid ETag/Last-Modified