Expires

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The HTTP Expires response header contains the date/time after which the response is considered expired in the context of HTTP caching.

The value 0 is used to represent a date in the past, indicating the resource has already expired.

Note: If there is a Cache-Control header with the max-age or s-maxage directive in the response, the Expires header is ignored.

Header type	Response header
Forbidden header name	No
CORS-safelisted response header	Yes

http

Expires: <day-name>, <day> <month> <year> <hour>:<minute>:<second> GMT

<day-name>: One of Mon, Tue, Wed, Thu, Fri, Sat, or Sun (case-sensitive).
<day>: 2 digit day number, e.g., "04" or "23".
<month>: One of Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec (case sensitive).
<year>: 4 digit year number, e.g., "1990" or "2016".
<hour>: 2 digit hour number, e.g., "09" or "23".
<minute>: 2 digit minute number, e.g., "04" or "59".
<second>: 2 digit second number, e.g., "04" or "59".
GMT: Greenwich Mean Time. HTTP dates are always expressed in GMT, never in local time.

http

Expires: Wed, 21 Oct 2015 07:28:00 GMT

Specification
HTTP Caching # field.expires

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