---
title: Using ETag Headers with Cloudflare · Cloudflare Cache (CDN) docs
description: ETag headers identify whether the version of a resource cached in the browser is the same as the resource at the origin 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.
source_url:
  html: https://e68be143.preview.developers.cloudflare.com/cache/reference/etag-headers/index.md
  md: https://e68be143.preview.developers.cloudflare.com/cache/reference/etag-headers/
---

ETag headers identify whether the version of a resource cached in the browser is the same as the resource at the origin 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.

Note

When using weak ETag headers, it is necessary to disable certain features such as [Email Obfuscation](https://developers.cloudflare.com/waf/tools/scrape-shield/email-address-obfuscation/) and [Automatic HTTPS Rewrites](https://developers.cloudflare.com/ssl/edge-certificates/additional-options/automatic-https-rewrites/) to prevent Cloudflare from removing the ETag headers set by your origin web server. For a comprehensive list of the features you need to disable, refer to the [Notes about end-to-end compression](https://developers.cloudflare.com/speed/optimization/content/compression/#notes-about-end-to-end-compression).

## Strong ETags

Strong ETag headers ensure the resource in browser cache and on the web server are byte-for-byte identical. Use [Cache Rules](https://developers.cloudflare.com/cache/how-to/cache-rules/) to enable strong ETag headers.

### Behavior with Respect Strong ETags enabled

When you enable **Respect Strong ETags** in a cache rule, Cloudflare will use strong ETag header validation to ensure that resources in the Cloudflare cache and on the origin server are byte-for-byte identical.

However, in some situations Cloudflare will convert strong ETags to weak ETags. For example, given the following conditions:

* **Respect Strong ETags** is enabled
* [Brotli compression](https://developers.cloudflare.com/speed/optimization/content/compression/) is enabled
* The origin server's response includes an `etag: "foobar"` strong ETag header

The Cloudflare network will take the following actions, depending on the visitor's `accept-encoding` header and the compression used in the origin server's response:

Enabling **Respect Strong ETags** in Cloudflare automatically disables Rocket Loader, Email Obfuscation, Automatic HTTPS Rewrites, and Mirage.

### Behavior with Respect Strong ETags disabled

When **Respect Strong ETags** is disabled, Cloudflare will preserve strong ETag headers set by the origin web server if all the following conditions apply:

* The origin server sends a response compressed using GZIP or Brotli, or an uncompressed response.
* If the origin server sends a compressed response, the visitor accepts the same compression (GZIP, Brotli), according to the `accept-encoding` header.
* [Rocket Loader](https://developers.cloudflare.com/speed/optimization/content/rocket-loader/) and [Email Obfuscation](https://developers.cloudflare.com/waf/tools/scrape-shield/email-address-obfuscation/) features are disabled.

In all other situations, Cloudflare will either convert strong ETag headers to weak ETag headers or remove the strong ETag. For example, given the following conditions:

* **Respect Strong ETags** is disabled
* [Brotli compression](https://developers.cloudflare.com/speed/optimization/content/compression/) is enabled
* The origin server's response includes an `etag: "foobar"` strong ETag header

The Cloudflare network will take the following actions, depending on the visitor's `accept-encoding` header and the compression used in the origin server's response:

## Important remarks

* You must set the value in a strong ETag header using double quotes (for example, `etag: "foobar"`). If you use an incorrect format, Cloudflare will remove the ETag header instead of converting it to a weak ETag. 

* If a resource is cacheable and there is a cache miss, Cloudflare does not send ETag headers to the origin server. This is because Cloudflare requires the full response body to fill its cache.
