> ## Documentation Index
> Fetch the complete documentation index at: https://docs.bunny.net/llms.txt
> Use this file to discover all available pages before exploring further.

# Do you support ETag?

## 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:

```http theme={null}
# Original Strong ETag from Origin
ETag: "123456789"

# Modified Weak ETag after Edge Compression
ETag: W/"123456789"
```