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AB-028
Vary Header
What it means
Your site tells caches that content varies based on the requested format.
Why it matters
Without a Vary header, caches may serve the wrong format to agents — JSON to someone who asked for HTML.
✗
What's wrong
No Vary header. Caches serve stale or wrong formats.
✓
What's right
Vary header ensures each agent gets the correct format from caches.
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