The HTTP Vary describes the parts of the request message (aside from the method and URL) that influenced the content of the response it occurs in. Including a Vary header ensures that responses are separately cached based on the headers listed in the Vary field. Most often, this is used to create a cache key when content negotiation is in use.

The same Vary header value should be used on all responses for a given URL, including Not Modified responses and the “default” response.

Syntax

Vary: *
Vary: <header-name>, …, <header-nameN>

Directives

• * (wildcard)

  • : Factors other than request headers influenced the generation of this response. Implies that the response is uncacheable.

  <header-name>

  • : A request header name that could have influenced the generation of this response.

Specifications

Browser compatibility

See also

• Content negotiation

• HTTP caching: Vary

• Understanding The Vary Header on smashingmagazine.com (2017)

• Best Practices for Using the Vary Header on fastly.com