Client hints
A set of HTTP headers and a JavaScript API through which the browser shares structured details like browser brand, version, and platform with websites.
Client hints are Chromium's structured replacement for user agent sniffing. Instead of parsing one long user agent string, servers read dedicated headers such as Sec-CH-UA (browser brands and versions), Sec-CH-UA-Platform (operating system), and Sec-CH-UA-Mobile, or query the navigator.userAgentData API in JavaScript. Low-entropy hints are sent by default; higher-entropy values like full version and architecture are only shared when a site requests them, which gives the browser some control over what it reveals.
Client hints matter because they created a second, independent source of identity claims. Fingerprinting and bot-detection scripts routinely compare the client hint values against the legacy user agent string, JavaScript navigator properties, and actual engine behavior. A browser whose user agent says Chrome 148 but whose Sec-CH-UA brands say something else is announcing that one of the layers has been modified. Keeping these layers in agreement is one of the harder problems in presenting a configured browser identity.
Oculr controls sec-ch-ua client hint metadata at the engine level, and both the user agent string and the client hint brands derive from the profile's pinned kernel version through a registry. Because the values come from the real engine version underneath, UA strings and client hints always match the engine actually running.
