Technical SEO
304 Not Modified
304 Not Modified tells a client making a conditional request that its cached representation remains valid and need not be retransmitted.
What it means
A client sends validators such as `If-None-Match` or `If-Modified-Since`; when the resource is unchanged, the server returns 304 without a message body and includes applicable metadata. The client then reuses its stored representation rather than navigating to another URL.
Why it matters
Correct revalidation saves bandwidth and server resources while allowing freshness checks. Google explicitly supports 304 for unchanged resources, but invalid validators or missing headers can cause stale content, unnecessary 200 transfers or confusing diagnostics.
Example
Googlebot requests an article with its previous ETag. The unchanged article returns 304 plus current cache metadata, so the cached body is reused; after an editorial update changes the ETag, the same condition produces a complete 200 response.
Common mistakes
Do not place a response body in 304, call it a URL redirect or return it to an unconditional request. Avoid weak change detection that reports not modified after content has actually changed.
How AYSA handles this
Signals reviewed
ETag, Last-Modified, conditional request headers, 304 metadata, unconditional 200 body
Problem AYSA can identify
AYSA can find resources whose validators never change, conditional requests that return full bodies or inconsistent cache metadata.
Recommendation prepared
The proposal aligns validator generation and response headers with the resource's real update lifecycle.
Approval preview
The user reviews paired conditional and unconditional requests and any caching-layer configuration before approval.
Execution
AYSA can adjust supported WordPress validators and accessible server cache rules; managed CDN validation may require its owner.
Verification
AYSA tests matching and stale validators and confirms correct 304 or 200 behavior without losing updated content.
Limits
Intermediary caches may implement additional validation logic that AYSA cannot change without provider access.
Sources and further reading
- MDN — 304 Not Modified — Web platform reference
- Google Crawling Infrastructure — Crawl budget management — Official platform documentation
- MDN — HTTP headers — Web platform reference
Written by Marius Dosinescu. Reviewed by AYSA SEO Editorial Team · 2026-07-28 00:00:00.
Quick answers
Frequently asked questions
Is 304 a redirect to a different URL?
No. It tells the client to reuse its cached representation of the same resource after a conditional validation request.
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