DateDate reports the time at which the message was generated (originated at the server). It appears mostly on responses, but the spec allows it on requests too, so it is defined for both directions.
The format is the fixed IMF-fixdate form, always in GMT (= UTC), including the weekday, day, month, year, and hour:minute:second (e.g. `Wed, 21 Oct 2026 07:28:00 GMT`).
The value must use RFC 9110's IMF-fixdate format. The zone is always the literal `GMT`; offsets (like +09:00) or local zones are not used. The obsolete RFC 850 and asctime formats are accepted for parsing compatibility, but new values must be generated as IMF-fixdate only.
Date is the anchor for cache freshness math. Caches combine it with `Age`, `Expires`, and `Cache-Control: max-age` to compute how old a resource is and when it expires. So a server clock that drifts (clock skew) can make caches treat a resource as fresh far too long, or expire it too early.
Most servers and frameworks add Date automatically, so you rarely set it by hand. But if a firewall, gateway, or embedded device has a wrong clock, absolute-time interpretation of `Expires` or `Retry-After` gets distorted, which is why keeping server time accurate via NTP matters.
Date: <day-name>, <day> <month> <year> <hour>:<minute>:<second> GMTe.g. Date: Wed, 21 Oct 2026 07:28:00 GMT