Sec-CH-UA
RequestActiveSec-CH-UA is a Client Hints header that provides a structured representation of the browser's brand and version. It replaces the full User-Agent string with a privacy-preserving alternative. The value contains a list of brand-version pairs – including a 'Not A Brand' entry to prevent fingerprinting via missing values.
Sec-CH-UA: "<brand>";v="<version>"[, ...]
Description
Sec-CH-UA replaces User-Agent's browser detection role. It provides: brand name, significant version, and a randomized 'Not A Brand' entry. Sec-CH-UA-Mobile indicates mobile. Sec-CH-UA-Platform indicates the OS. These are low-entropy hints sent by default; higher-entropy hints (Sec-CH-UA-Arch, Sec-CH-UA-Full-Version-List) require Accept-CH opt-in. Chrome, Edge, and Opera send Sec-CH-UA natively.
Examples
Chrome on desktop
http
Sec-CH-UA: "Not)A;Brand";v="99", "Google Chrome";v="127", "Chromium";v="127"
Sec-CH-UA-Mobile: ?0
Sec-CH-UA-Platform: "macOS"