Headers: Sec-CH-UA-Form-Factors

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.

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Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The HTTP Sec-CH-UA-Form-Factors request header is a user 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

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 the Sec-CH-UA-Form-Factors header by including the Accept-CH in a response to any request from the client, using the name of the desired header as a token:

HTTP/1.1 200 OK
Accept-CH: Sec-CH-UA-Form-Factors

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

GET /my/page HTTP/1.1
Host: example.site

Sec-CH-UA-Mobile: ?0
Sec-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.

Specifications

Specification
User-Agent Client Hints> # sec-ch-ua-form-factors>

Browser compatibility

	Desktop					Mobile
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	WebView on iOS
`Sec-CH-UA-Form-Factors`	124	124	No	110	No	124	No	82	No	23.0	124	No