breadcrumbs: updates > page_name: ua-reduction title: User-Agent Reduction
May 24, 2021: The chrome://flags#freeze-user-agent flag was renamed to chrome://flags/#reduce-user-agent in Chrome 93 and the values were updated to align with the plan below (also testable via --enable-features=ReduceUserAgent).
September 16, 2021: Chrome milestones were added to reflect https://blog.chromium.org/2021/09/user-agent-reduction-origin-trial-and-dates.html.
Reduction Preparation
Phase 1: Warn about accessing navigator.userAgent, navigator.appVersion, and navigator.platform in DevTools, beginning in M92. Phase 2: Chrome 95 to Chrome 100 Launch an Origin Trial for sites to opt into the final reduced UA string for testing and feedback, for at least 6 months.
Reduction Rollout
Phase 3: Chrome 100 Launch a reverse Origin Trial, for instances where a site may need more time for migration, for at least 6 months. Phase 4: Chrome 101 Ship reduced Chrome MINOR.BUILD.PATCH version numbers (“0.0.0”). Once rolled-out, the reduced UA string would apply to all page loads on desktop and mobile OSes that do not opt into the reverse Origin Trial. Phase 5: Chrome 107 Begin roll-out of reduced Desktop UA string and related JS APIs (navigator.userAgent, navigator.appVersion, navigator.platform). Once rolled-out, the reduced UA string would apply to all page loads on desktop OSes that do not opt into the reverse Origin Trial. Phase 6: Chrome 110 Begin roll-out of reduced Android Mobile (and Tablet) UA string and related JS APIs. Once rolled-out, the reduced UA string would apply to all page loads on Android that do not opt into the reverse Origin Trial.
Reduction Completion Phase 7: Chrome 113 reverse Origin Trial ends and all page loads receive the reduced UA string and related JS APIs.
The unified format that covers all platforms post-UA Reduction looks like so:
Mozilla/5.0 () AppleWebKit/537.36 (KHTML, like Gecko) Chrome/.0.0.0 Safari/537.36
The Chrome Desktop User Agent string currently uses the following format:
Mozilla/5.0 (; ) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/. Safari/537.36
Post UA-Reduction, the new format will be:
Mozilla/5.0 () AppleWebKit/537.36 (KHTML, like Gecko) Chrome/.0.0.0 Safari/537.36
The Chrome Mobile and Tablet User Agent strings use the following format:
Mozilla/5.0 (Linux; Android ; ) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/. Safari/537.36
Post UA-Reduction, the new format will be:
Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/.0.0.0 Safari/537.36
Tokens
Description
Represents Android major version
Represents Android device model.
Represents the Chrome MINOR.BUILD.PATCH version numbers.
Represents the device operating system and (optionally) CPU architecture.
Represents the underlying device platform.
Post-Reduction Tokens
Represents device form-factor.
The possible values are:
“Mobile” “” (empty string, used by Tablets and Desktop)
Represents the Chrome major version.
The intersection of , , , and , depending on device.
The possible desktop values* are:
Windows NT 10.0; Win64; x64 Macintosh; Intel Mac OS X 10_15_7 X11; Linux x86_64 X11; CrOS x86_64
The possible mobile values* are:
Linux; Android 10; K
*Note that these strings are literal values; they will not update even if a user is on an updated operating system or device.
In Phase 4 we change the token to “0.0.0”.
Desktop (user on Windows 8.1, for example)
Phase 3 UA
Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.1234.56 Safari/537.36
Phase 4 UA
Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Safari/537.36
Mobile (user on Samsung Galaxy, for example)
Phase 3 UA
Mozilla/5.0 (Linux; Android 9; SM-A205U) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.1234.56 Mobile Safari/537.36
Phase 4 UA
Mozilla/5.0 (Linux; Android 9; SM-A205U) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Mobile Safari/537.36
Tablet (user on Samsung Galaxy, for example)
Phase 3 UA
Mozilla/5.0 (Linux; Android 9; SM-T810) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.1234.56 Safari/537.36
Phase 4 UA
Mozilla/5.0 (Linux; Android 9; SM-T810) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Safari/537.36
In Phase 5 we change the and tokens from their platform-defined values to the relevant token value (which will never change).
Note: There may not be user-visible changes here, unless the user was on a lower version.
Also note that the macOS platform version was already capped to 10_15_7 in Chrome 90 for site compatibility reasons.
Desktop (user on Windows 8.1, for example)
Phase 4 UA
Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Safari/537.36
Phase 5 UA
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Safari/537.36
Mobile (user on Samsung Galaxy, for example)
Phase 4 UA
Mozilla/5.0 (Linux; Android 9; SM-A205U) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Mobile Safari/537.36
Phase 5 UA
(No changes for Mobile UAs in Phase 5)
Tablet (user on Samsung Galaxy, for example)
Phase 4 UA
Mozilla/5.0 (Linux; Android 9; SM-T810) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Safari/537.36
Phase 5 UA
(No changes for Tablet UAs in Phase 5)
In Phase 6, we change the token to “K” and change the token to a static “10” string.
Desktop (user on Windows 8.1, for example)
Phase 5 UA
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Safari/537.36
Phase 6 UA
(No changes for Desktop UAs from Phase 5)
Mobile (user on Samsung Galaxy, for example)
Phase 5 UA
Mozilla/5.0 (Linux; Android 9; SM-A205U) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Mobile Safari/537.36
Phase 6 UA
Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Mobile Safari/537.36
Tablet (user on Samsung Galaxy, for example)
Phase 5 UA
Mozilla/5.0 (Linux; Android 9; SM-T810) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Safari/537.36
Phase 6 UA
Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Safari/537.36
Desktop (user on Windows 8.1, for example)
Old UA
Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.1234.56 Safari/537.36
Final Reduced UA
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Safari/537.36
Mobile (user on Samsung Galaxy, for example)
Old UA
Mozilla/5.0 (Linux; Android 9; SM-A205U) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.1234.56 Mobile Safari/537.36
Final Reduced UA
Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Mobile Safari/537.36
Tablet (user on Samsung Galaxy, for example)
Old UA
Mozilla/5.0 (Linux; Android 9; SM-T810) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.1234.56 Safari/537.36
Final Reduced UA
Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.0.0 Safari/537.36
Platform
Reduced value
macOS
MacIntel
Windows
Win32
Chrome OS
Linux x86_64
Linux
Linux x86_64
Android
Linux armv81
navigator.appVersion is effectively an alias of navigator.userAgent (it’s everything after “Mozilla/”).
To avoid confusion and reduce implementation complexity, we aim to follow the same plan for navigator.userAgent.