Sec-CH-UA-WoW64 header

Limited availability

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

See full compatibility

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-WoW64 request header is a user agent client hint indicating if a 32-bit user-agent application is running on a 64-bit Windows machine.

WoW64 was commonly used to know which NPAPI plugin installer should be offered for download. This client hint header is used for backwards compatibility considerations, to provide a one-to-one mapping from the user-agent string of certain browsers to UA client hints.

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

Syntax

http

Sec-CH-UA-WoW64: <boolean>

Directives

<boolean>: ?1 indicates that the user agent's binary is running in 32-bit mode on 64-bit Windows (true), while ?0 means that it is not (false).

Examples

Using Sec-CH-UA-WoW64

A server requests the Sec-CH-UA-WoW64 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

HTTP/1.1 200 OK
Accept-CH: Sec-CH-UA-WoW64

The client may choose to provide the hint, and add the Sec-CH-UA-WoW64 header to subsequent requests. Adding Sec-CH-UA-WoW64: ?1 means the user agent's binary is running in 32-bit mode on 64-bit Windows:

http

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

Sec-CH-UA-WoW64: ?1
Sec-CH-UA-Platform: "Windows"
Sec-CH-UA-Form-Factors: "Desktop"

Specifications

Specification
User-Agent Client Hints # sec-ch-ua-wow64

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-WoW64` request header Experimental	Chrome – Full support Chrome 100 (Release date: 2022-03-29) footnote Full support	Edge – Full support Edge 100 (Release date: 2022-04-01) footnote Full support	Firefox – No support Firefox footnote No support	Opera – Full support Opera 86 (Release date: 2022-04-20) footnote Full support	Safari – No support Safari footnote No support	Chrome Android – Full support Chrome Android 100 (Release date: 2022-03-29) footnote Full support	Firefox for Android – No support Firefox for Android footnote No support	Opera Android – Full support Opera Android 69 (Release date: 2022-05-09) footnote Full support	Safari on iOS – No support Safari on iOS footnote No support	Samsung Internet – Full support Samsung Internet 23 (Release date: 2023-10-18) footnote Full support	WebView Android – Full support WebView Android 100 (Release date: 2022-03-29) footnote Full support	WebView on iOS – No support WebView on iOS footnote No support

Tip: you can click/tap on a cell for more information.

Full support: Full support
No support: No support
: Experimental. Expect behavior to change in the future.

Sec-CH-UA-WoW64 header

Syntax

Directives

Examples

Using Sec-CH-UA-WoW64

Specifications

Browser compatibility

Legend

See also