one check
What is my user agent?
The name your browser sends with every request, what it claims, and whether three other sources back it up.
Reading your user agent
Why does my user agent say Windows NT 10.0 on Windows 11?
Microsoft kept the version number at 10.0 for Windows 11, and Chromium's reduced format freezes it for every Windows anyway. A site that needs to tell the two apart asks for the platform version client hint, where Windows 11 reports 13 or higher (Microsoft's guide (opens in a new tab)).
Why does every browser call itself Mozilla and Safari?
In the 1990s sites served their best pages only to Netscape, whose string began with Mozilla, so every other browser started claiming it too. Each new browser since has copied the tokens sites test for, which is why a Chrome string names Mozilla, KHTML, Gecko and Safari before it names Chrome.
Can I change my user agent, and does it help?
Every browser lets you: Chrome in its developer tools under Network conditions, automation tools with one setting. It rarely helps against a bot check, because the client hints, the connection handshake and the rendering still describe the real browser, and a disagreement between them is easier to spot than the original string. The section above shows that comparison for your own browser.
What is the reduced user agent format?
Between versions 101 and 113 Chromium replaced the operating system version with a fixed value and set the minor browser version to zero, so the string tells sites less by default. The exact values moved to client hints, which a site has to ask for (Chromium's announcement (opens in a new tab)).
What this one page cannot tell you
The string is compared with the header, the client hints and the connection, but not with the rendering, the fonts or the timing a site can also read.
The interesting part is usually not a single value but the disagreement between two. The full check reads all five layers and shows you where they contradict each other.