field Registered
Verified 2026-09-18 · registry updated
2026-08-28If-None-Match
Makes a request conditional on the current entity tag not matching.
Use it for cache revalidation or create-if-absent operations. A matching GET or HEAD normally produces 304; a matching unsafe request produces 412.
httpheadercacheconditional
Reference (http)
If-None-Match: "user-42-v7"
Use it for cache revalidation or create-if-absent operations. A matching GET or HEAD normally produces 304; a matching unsafe request produces 412.
Common mistakes
- Applying it without understanding the different GET/HEAD and write semantics.
IANA registry: http-fields/field-names
Registry reference: RFC 9110, Section 13.1.2: HTTP Semantics