HTTP Headers

Sec CH UA WoW64

HTTP Header

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

Sec-CH-UA-WoW64: <boolean>

Directives

<boolean>

The ?1 indicates that the user’s system is a 32-bit binary running on a 64-bit Windows environment, which is considered true, whereas ?0 means it is not, indicating false.

Example

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"

How to Modify Header using Requestly

Requestly is a powerful Chrome extension that allows you to modify HTTP headers, including the Sec-CH-UA-WoW64 header. This can help you simulate different browser and device environments to test how websites respond to these signals. Steps to Modify the Sec CH UA WoW64 Header:

Install and open the Requestly Chrome extension. You can find it on the Chrome Web Store.
Create a new rule: Click on “Create Rule” and choose “Modify Headers” from the list of available rule types.
Add a new header modification:
- Under “Action”, select “Add” or “Override”.
- In the “Header Name” field, enter Sec-CH-UA-WoW64.
- In the “Header Value” field, enter your desired value (e.g., “true” or “false”).
Set the URL condition: Specify the URL or pattern where this header change should apply (e.g., https://your-website.com/*).
Save the rule.

Once set up, Requestly will inject the modified Sec-CH-UA-WoW64 header into all matching requests, helping you test how your site or application adapts to different Windows-on-Windows 64-bit environments. You might need to modify this header to check how your website behaves on different Windows emulation layers, which can affect feature detection or content delivery. It helps ensure compatibility and optimize user experience across diverse devices.