How Expires works
The HTTP/1.0 way to set a cache lifetime. If the response also has Cache-Control: max-age (or s-maxage), Expires is ignored. An invalid date, such as 0, means “already expired”. Absolute dates depend on clocks being right, which is why max-age replaced it.
Examples
Expires: Thu, 01 Jan 2027 00:00:00 GMTExpires: 0Check it
curl -sI https://example.com | grep -i '^expires:'Paste a full set of response headers into the HTTP header checker to get every header explained and common mistakes flagged.
Related headers
- Cache-Control: tells browsers, CDNs and proxies whether a response may be stored, by whom, and for how long.
- Age: tells how many seconds a response has spent in a cache (usually a CDN) since it was fetched from the origin.
- Last-Modified: says when the resource was last changed, for revalidation and heuristic caching.
More caching headers
ETag , If-None-Match , If-Modified-Since , Vary .
Sources
Spotted a mistake? Email hello@devtoolsmith.com and we’ll fix it.
Frequently asked questions
What does the Expires header do?
The Expires response header gives an absolute date after which the response is stale. The HTTP/1.0 way to set a cache lifetime. If the response also has Cache-Control: max-age (or s-maxage), Expires is ignored. An invalid date, such as 0, means “already expired”. Absolute dates depend on clocks being right, which is why max-age replaced it.
How do I see the Expires header?
Run "curl -sI https://example.com" to print a response’s headers, or open the Network tab in your browser’s dev tools and select the request. Paste the headers into the HTTP header checker on this site to get each one explained.