Vary Header

What is the Vary header?

The Vary response header, defined in RFC 9110, names the request headers that a cache must consider before serving a stored response. It tells caches that the same URL can produce different representations depending on those headers.

API Usage & Best Practices

• Correct content negotiation: Listing Accept, Accept-Encoding, or Accept-Language ensures a client asking for JSON is never served a cached HTML response, and a gzip-capable client is not handed a brotli body it cannot read.
• Protect private data: Including Authorization prevents a shared cache from returning one user’s personalized response to another.
• Use the wildcard sparingly: Vary: * means the response varies on factors outside the request headers, which effectively makes it uncacheable by shared caches.

Examples

HTTP/1.1 200 OK
Content-Type: application/json
Vary: Accept, Accept-Encoding