files/en-us/web/http/reference/headers/sec-ch-ua-wow64/index.md
{{SecureContext_Header}}{{SeeCompatTable}}
The HTTP Sec-CH-UA-WoW64 {{Glossary("Request header", "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.
<table class="properties"> <tbody> <tr> <th scope="row">Header type</th> <td> {{Glossary("Request header")}}, <a href="/en-US/docs/Web/HTTP/Guides/Client_hints">Client hint</a> </td> </tr> <tr> <th scope="row">{{Glossary("Forbidden request header")}}</th> <td>Yes (<code>Sec-</code> prefix)</td> </tr> </tbody> </table>Sec-CH-UA-WoW64: <boolean>
<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).A server requests the Sec-CH-UA-WoW64 header by including the {{HTTPHeader("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-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:
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}}
{{Compat}}