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Using ETag Headers with Cloudflare

ETag headers identify whether the version of a resource cached in the browser is the same as the resource at the web server. A visitor’s browser stores ETags. When a visitor revisits a site, the browser compares each ETag to the one it stored. Matching values cause a 304 Not-Modified HTTP response that indicates the cached resource version is current. Cloudflare supports both strong and weak ETags configured at your origin web server.

​​ Weak ETags

Weak ETag headers indicate a cached resource is semantically equivalent to the version on the web server but not necessarily byte-for-byte identical. Cloudflare supports weak ETag headers on all plans.

​​ Strong ETags

Strong ETag headers ensure the resource in browser cache and on the web server are byte-for-byte identical. Domains on Enterprise plans enable strong ETag headers via a Respect Strong ETags Page Rule and lower plans customers can enable strong ETag headers using Cache Rules. Otherwise, strong ETag headers are converted to weak ETag headers. Also, set a strong ETag header in quotes (Etag: “example”) or Cloudflare removes the ETag instead of converting it to a weak ETag. 

Without a Page Rule, Cloudflare preserves strong ETags set by the origin web server if: