Adding 4 new recent feature additions / changes to the User-Agent client hints API.


1. Sec-CH-UA-Bitness: adds a new high-entropy hint to expose the OS bitness. 2. Make Sec-CH-UA-Platform a low-entropy hint: OS is passively observable at the TCP level anyways, so we should expose this by default as a low-entropy hint. 3. Include low-entropy hints by default in UADataValues (returned by getHighEntropyValues()). If a hint moves from high to low-entropy, this future proofs and code relying on as 4. Add a toJSON method to NavigatorUAData’s IDL. Technically a bugfix, but it is an API change (instead of returning {}, JSON.stringify(navigator.userAgentData)) will now be useful)


Editor's draft

Status in Chromium


No active development in:

  • Chrome for desktop release No active development
  • Chrome for Android release 93

Consensus & Standardization

After a feature ships in Chrome, the values listed here are not guaranteed to be up to date.


Intent to Prototype url

Intent to Prototype thread


This is 3 incremental additions to the existing User-Agent Client Hints API.

Last updated on 2021-06-21