The line your browser announces
Every time your browser requests a page, it sends a User-Agent header — a text string identifying the browser, its version, and the operating system. Servers use it to serve compatible content and gather analytics.
Why it looks like nonsense
A modern user-agent might read like Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/.... The mess is historical: browsers copied each other's identifiers over decades to avoid being served degraded content, so today's strings contain the names of browsers that aren't even running.
What it reveals — and doesn't
- Reveals: browser family and version, OS, and whether you're on mobile or desktop.
- Doesn't reveal: your identity, your name, or your exact device model in most cases.
It's one signal websites combine with others (IP, screen size) for analytics or fingerprinting, but on its own it's fairly generic — millions of people share the same string.
Can you change it?
Yes — browser dev tools and extensions let you spoof a user-agent, which is handy for testing how a site behaves on different devices. Note that user-agent is gradually being reduced by browsers in favor of more privacy-conscious 'client hints'.
Frequently Asked Questions
Can a website identify me from my user-agent?
Not by itself — millions of people share identical user-agent strings. It's a generic signal, though it can be combined with others for fingerprinting.
Why does Chrome's user-agent mention Mozilla and Safari?
Historical compatibility. Browsers copied each other's identifiers over the years so servers wouldn't send them degraded content.
Is it safe to change my user-agent?
Yes, it's commonly done for testing. It only changes how sites perceive your browser, not your actual browser or device.