Vary header

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 Vary response header 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 304 Not Modified responses and the "default" response.

Header type	Response header
Forbidden request header	No

Syntax

http

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.