Understanding the user agent string
The user agent(UA) is sent in an HTTP header with every page request. It tells the server which browser and platform you're using so it can serve compatible pages. A typical UA packs several tokens: a legacy Mozilla/5.0 prefix, the platform (e.g. Windows NT 10.0), the engine (AppleWebKit), and the browser and version (Chrome/124.0).
What it's used for
- Serving the right layout for desktop vs mobile.
- Feature detection fallbacks and compatibility fixes.
- Analytics, such as counting which browsers visitors use.
- Bot detection and, sometimes, fingerprinting.
Related tools
See everything else your browser exposes with Browser Info, check your public IP address, or test for WebRTC IP leaks.
Frequently asked questions
What is a user agent?
A user agent is a text string your browser sends with every request to identify itself. It includes the browser name and version, the rendering engine, and your operating system, so servers can deliver compatible content.
Why does my user agent look so complicated?
For historical compatibility reasons, modern user agents include tokens like 'Mozilla/5.0' and 'like Gecko' even on browsers that aren't Mozilla or Gecko-based. It's legacy baggage every browser still carries.
Can I change my user agent?
Yes. Browser developer tools and extensions let you spoof your user agent, which is useful for testing. Note that many other signals (see our Browser Info tool) can still reveal your real browser.
Is my user agent unique to me?
Not on its own. Plenty of people share the same user agent. But combined with your other browser attributes, it adds to a fingerprint that can be quite identifying.