The Key HTTP Response Header Field

Document Type Replaced Internet-Draft (candidate for httpbis WG)
Authors Roy Fielding  , Mark Nottingham 
Last updated 2015-10-14 (latest revision 2015-09-23)
Replaced by draft-ietf-httpbis-key
Stream Internet Engineering Task Force (IETF)
Intended RFC status (None)
Expired & archived
pdf htmlized (tools) htmlized bibtex
Stream WG state Call For Adoption By WG Issued
Document shepherd No shepherd assigned
IESG IESG state Replaced by draft-ietf-httpbis-key
Consensus Boilerplate Unknown
Telechat date
Responsible AD (None)
Send notices to (None)

This Internet-Draft is no longer active.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 ([RFC7234], 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 (

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)