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

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

The Sec-CH-UA-Bitness user agent client hint request header provides the "bitness" of the user-agent's underlying CPU architecture. This is the size in bits of an integer or memory address—typically 64 or 32 bits.

This might be used by a server, for example, to select and offer the correct binary format of an executable for a user to download.

Header type Request header, Client hint
Forbidden header name yes


Sec-CH-UA-Bitness: <bitness>



A string indicating the underlying platform architecture bitness, such as: "64", "32".


A server requests the Sec-CH-UA-Bitness 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-Bitness

The client may choose to provide the hint, and add the Sec-CH-UA-Bitness header to subsequent requests. For example, on a Windows based 64-bit computer, the client might add the header as shown:

GET /GET /my/page HTTP/1.1

Sec-CH-UA: " Not A;Brand";v="99", "Chromium";v="96", "Google Chrome";v="96"
Sec-CH-UA-Mobile: ?0
Sec-CH-UA-Platform: "Windows"
Sec-CH-UA-Bitness: "64"


User-Agent Client Hints
# sec-ch-ua-bitness

Browser compatibility

BCD tables only load in the browser

See also