The Key HTTP Response Header Field

Document Type Expired Internet-Draft (httpbis WG)
Authors Roy Fielding  , Mark Nottingham 
Last updated 2018-04-03 (latest revision 2016-03-01)
Replaces draft-fielding-http-key
Stream IETF
Intended RFC status Proposed Standard
Expired & archived
pdf htmlized (tools) htmlized bibtex
Stream WG state Dead WG Document
Document shepherd Martin Thomson
IESG IESG state Expired
Consensus Boilerplate Unknown
Telechat date
Responsible AD (None)
Send notices to "Martin Thomson" <>

This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


The 'Key' header field for HTTP responses allows an origin server to describe the secondary cache key (RFC 7234, Section 4.1) for a resource, by conveying what is effectively a short algorithm that can be used upon later requests to determine if a stored response is reusable for a given request. Key has the advantage of avoiding an additional round trip for validation whenever a new request differs slightly, but not significantly, from prior requests. Key also informs user agents of the request characteristics that might result in different content, which can be useful if the user agent is not sending request header fields in order to reduce the risk of fingerprinting.


Roy Fielding (
Mark Nottingham (

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