Expires Header

What is the Expires header?

The Expires response header, defined in RFC 9111, contains an HTTP-date that marks when a response should no longer be considered fresh. After that moment, a cache must revalidate the resource before reusing it.

API Usage & Best Practices

• Superseded by Cache-Control: When both Expires and Cache-Control: max-age are present, the relative max-age directive wins and Expires is ignored.
• Invalid dates mean stale: A malformed date, or the value 0, is treated as already expired, forcing revalidation on the next request.

Examples

HTTP/1.1 200 OK
Expires: Thu, 09 Jul 2026 12:00:00 GMT