What are User-Agent Client Hints (UA-CH)?

User-Agent Client Hints replace parts of the freeform User-Agent with structured, requestable fields: the brand list and versions, platform and version, architecture and bitness, a mobile flag, and more — available both as request headers and via navigator.userAgentData.

Their value to detection is cross-checking: the UA-CH fields must agree with the classic User-Agent, with the TLS/HTTP-2 stack, and with JS-observable platform properties. Spoofing the UA string but leaving UA-CH (or vice-versa) inconsistent is a common mistake.

Clearcote sets the UA and UA-CH together from one persona — brand, version, platform, bitness — so they never disagree. See fingerprint flags.