All HTTP status codes

HTTP 304 Not Modified

Redirection

The cached copy the client holds is still valid — the server sends no body. The result of conditional requests with If-None-Match (ETag) or If-Modified-Since.

Defined in RFC 9110

Common causes

  • Conditional GETs from browsers and CDNs with fresh caches

How to fix it

  1. Nothing to fix — this saves bandwidth

  2. If content never updates for users, check that ETags change when content changes (beware multi-server ETag mismatches)

Related status codes

200 OK

The request succeeded. The response body contains the result — a page for GET, the operation outcome for POST.

412 Precondition Failed

A conditional header (If-Match, If-Unmodified-Since…) evaluated to false — the resource changed since the client last saw it.

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