Sec-CH-UA-WoW64

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 header name 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

Report problems with this compatibility data on GitHub
desktopmobile
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

Legend

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.

See also