HTTP Caching HTTP responses Obsolete, redundant and non-standard headers


  • Expires — specifies date when the resource becomes stale. It relies on servers and clients having accurate clocks and supporting time zones correctly. Cache-control: max-age takes precedence over Expires, and is generally more reliable.

  • post-check and pre-check directives are non-standard Internet Explorer extensions that enable use of stale responses. The standard alternative is stale-while-revalidate.

  • Pragma: no-cache — obsoleted in 1999. Cache-control should be used instead.