What is an ETag?
The ETag (Entity Tag) header is an HTTP response header used to uniquely identify a specific version of a file. It allows web browsers and CDNs to quickly determine whether a cached copy of a file is still identical to the one on the origin server.
If a file changes, its ETag changes as well, making it a highly effective tool for validation, maximizing cache efficiency, and minimizing origin bandwidth usage.
How Bunny.net Handles ETag Headers
Bunny.net fully supports the ETag header out of the box, with a few important behavior considerations depending on your configuration:
Origin Passthrough
If your origin server includes an ETag header in its response and the Optimize for large media delivery setting is disabled in your Pull Zone, Bunny.net will pass the ETag through to the client and cache the resource accordingly.
Smart Compression Adjustments
When Bunny.net applies edge compression to a file (such as Brotli or Gzip), the original strong ETag will automatically be converted into a weak ETag.
When this happens, an upstream W/ prefix is added to the start of the header string:
# Original Strong ETag from Origin
ETag: "123456789"
# Modified Weak ETag after Edge Compression
ETag: W/"123456789"
Last modified on July 3, 2026
