topic
Verified 2026-09-18Warning Header and Legacy Cache Diagnostics
The Warning response field historically reported cache and representation conditions using numeric warning codes.
Prefer current Cache-Control, Age, and response semantics for new designs. If a legacy client requires Warning, preserve its quoted text carefully and do not treat intermediary diagnostics as an authoritative application decision.
httpcacheheaderlegacy
Reference (http)
Warning: 110 - "Response is stale" Age: 3600
Prefer current Cache-Control, Age, and response semantics for new designs. If a legacy client requires Warning, preserve its quoted text carefully and do not treat intermediary diagnostics as an authoritative application decision.
Common mistakes
- Adding Warning to modern responses as a replacement for Cache-Control, or exposing internal cache implementation details to users.