What is a user agent?
A user agent is the text your browser sends with every request to identify itself, for example:
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/129.0.0.0 Safari/537.36Websites use it to serve compatible pages, collect analytics and detect bots. The odd mix of names (Mozilla, AppleWebKit, Gecko, Safari) is historical: browsers copied each other's tokens to avoid being blocked by sites that sniffed for specific browsers.
User-Agent Client Hints
Chromium-based browsers now "freeze" much of the user agent (for example Windows 11 still reports Windows NT 10.0) and offer more precise data through Client Hints headers such as Sec-CH-UA and Sec-CH-UA-Platform, which sites must request explicitly. That reduces passive fingerprinting. You can see any hints your browser sent in the table above.
What else can websites learn about your browser?
Beyond the user agent, any page can read your screen size, language, time zone, number of CPU cores and whether cookies are enabled. Combined, these signals can create a "fingerprint" that can be fairly unique. Privacy-focused browsers reduce fingerprinting by standardising or randomising these values. Your IP address is also visible to every site you visit unless you use a VPN or Tor. See how to hide it.
Frequently asked questions
Can I change my user agent?
Yes. In Chrome and Edge open DevTools, then Network conditions, and untick "Use browser default". Firefox has general.useragent.override in about:config. Extensions can also do it.
Does the user agent reveal who I am?
Not by itself. It describes your software, not your identity, but it contributes to browser fingerprinting.