Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.
The Sec-CH-UA user agent client hint request header provides the user-agent's branding and significant version information.
| Header type | Request header, Client hint |
|---|---|
| Forbidden header name | yes |
The Sec-CH-UA header provides the brand and significant version for each brand associated with the browser in a comma-separated list.
A brand is a commercial name for the user agent like: Chromium, Opera, Google Chrome, Microsoft Edge, Firefox, and Safari. A user agent might have several associated brands. For example, Opera, Chrome, and Edge are all based on Chromium, and will provide both brands in the Sec-CH-UA header.
The significant version is the "marketing" version identifier that is used to distinguish between major releases of the brand. For example a Chromium build with full version number "96.0.4664.45" has a significant version number of "96".
The header therefore allows the server to customize its response based on both shared brands and on particular customizations in their respective versions.
Sec-CH-UA is a low entropy hint. Unless blocked by a user agent permission policy, it is sent by default, without the server opting in by sending Accept-CH.
The header may include "fake" brands in any position and with any name. This is a feature designed to prevent servers from rejecting unknown user agents outright, forcing user agents to lie about their brand identity.
Note: Sec-CH-UA-Full-Version-List is the same as Sec-CH-UA, but includes the full version number rather than the significant version number for each brand.