topic
Verified 2026-09-18

Cache-Control: must-understand

Allows caching only when the cache understands the response status code.

must-understand (RFC 9111) lets caches store unusual statuses only if they implement their semantics, paired with no-store as the fallback for caches that do not.

httpcacheheaderdirective

Reference (http)

Cache-Control: must-understand, no-store

must-understand (RFC 9111) lets caches store unusual statuses only if they implement their semantics, paired with no-store as the fallback for caches that do not.

Common mistakes

  • Sending must-understand without no-store, which changes nothing for caches that ignore the status.

Sources

Permalink: https://merginit.com/reference/http/directive-must-understand