allows an origin server to describe the cache key for a negotiated response: a short algorithm that can be used upon later requests to determine if the same response is reusable.
Quick facts
Description
allows an origin server to describe the cache key for a negotiated response: a short algorithm that can be used upon later requests to determine if the same response is reusable.
Syntax
Key: <value>
Frequently asked questions
allows an origin server to describe the cache key for a negotiated response: a short algorithm that can be used upon later requests to determine if the same response is reusable.
It is classified as a request header and can appear in requests or responses depending on context.
Sources & standards
Updated 2026-09-13
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