HTTP 304 Not Modified

What HTTP 304 means

HTTP 304 Not Modified is the answer to a conditional request. The client says “I have a copy from this date” (If-Modified-Since) or “with this fingerprint” (If-None-Match), and the server confirms the copy is still current by replying 304 with no body.

This mechanism — cache revalidation — is what makes repeated page loads fast: the browser re-downloads only what changed, and everything else costs a single small round trip.

Common causes of 304 responses

• The browser revalidated a cached page, script or image and it had not changed.
• A CDN edge revalidated its stored object against the origin.
• An API client used ETags to poll a resource cheaply.

Good practices for developers

• Serve stable ETag or Last-Modified headers so clients can revalidate at all.
• Do not include a response body with 304 — the client explicitly has it already.
• Beware of ETags that change on every response (e.g. from load-balanced servers with per-node hashes): they silently disable revalidation.

Example response

GET /styles.css HTTP/1.1
If-None-Match: "abc123"

HTTP/1.1 304 Not Modified
ETag: "abc123"
Cache-Control: max-age=3600

SEO impact

304 responses are good for SEO performance: Googlebot uses conditional requests heavily, and correct revalidation lets it crawl more of your site for the same budget. Broken validators force full re-downloads on every crawl.

FAQ