Sec-CH-UA-Form-Factors header

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

Secure context: This feature is available only insecure contexts (HTTPS), in some or allsupporting browsers.

Experimental:This is anexperimental technology
Check theBrowser compatibility table carefully before using this in production.

The HTTPSec-CH-UA-Form-Factorsrequest header is auser agent client hint which provides information on the user-agent's device form factor.

Header type	Request header,Client hint
Forbidden request header	Yes (`Sec-` prefix)

Syntax

http

Sec-CH-UA-Form-Factors: <form-factor>Sec-CH-UA-Form-Factors: <form-factor>, …, <form-factor>

Directives

<form-factor>

A string indicating a common device form factor.All applicable form factors can be included.The meanings of the allowed values are:

"Desktop": A user-agent running on a personal computer.
"Automotive": A user-agent embedded in a vehicle, where the user may be responsible for operating the vehicle and have limited ability to interact.
"Mobile": Small, touch-oriented device typically carried on a user's person.
"Tablet": A touch-oriented device larger than"Mobile" and not typically carried on a user's person.
"XR": Immersive devices that augment or replace the environment around the user.
"EInk": A device characterized by slow screen updates and limited or no color resolution.
"Watch": A mobile device with a tiny screen (typically less than 2 inches), carried in such a way that the user can glance at it quickly.

Examples

Using Sec-CH-UA-Form-Factors

A server requests theSec-CH-UA-Form-Factors header by including theAccept-CH in aresponse to any request from the client, using the name of the desired header as a token:

http

HTTP/1.1 200 OKAccept-CH: Sec-CH-UA-Form-Factors

The client may choose to provide the hint, and add theSec-CH-UA-Form-Factors header to subsequent requests.For example, the client might add the header as shown:

http

GET /my/page HTTP/1.1Host: example.siteSec-CH-UA-Mobile: ?0Sec-CH-UA-Form-Factors: "EInk"

In this case,"EInk" means that the device is characterized by slow screen updates and limited color resolution, and as such, responses may differ depending on this hint.