IP and InternetWhat a user agent is for
When your browser asks a server for a page, it introduces itself with a line called the user agent. Servers use it to send the right version of a page (mobile or desktop), to work around the quirks of old browsers, and to count which browsers their visitors use. Search engine crawlers and other automated programs announce themselves the same way.
Reading the line
A typical line from Chrome on Windows looks like this:
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36
| Part | What it says |
|---|---|
| Mozilla/5.0 | A leftover from the 1990s that every browser still sends so that old servers do not turn it away. It means nothing today |
| (Windows NT 10.0; Win64; x64) | The system: Windows 10 or 11, 64-bit |
| AppleWebKit/537.36 (KHTML, like Gecko) | The engine family the browser descends from. More history than fact |
| Chrome/130.0.0.0 | The browser and its main version |
| Safari/537.36 | Another leftover, kept so that sites written for Safari accept Chrome |
The line reads oddly because each new browser, to avoid being shut out by sites that checked for a rival's name, copied the rival's words and added its own. Edge adds Edg/, Opera adds OPR/, Samsung Internet adds SamsungBrowser/. That is why the decoder has to look for the most specific name first.
What it can no longer tell you
Browsers have been cutting detail out of the line, because it helped fingerprinting.
- Windows 10 and Windows 11 both say "Windows NT 10.0". The line alone cannot tell them apart.
- Mac browsers say "Mac OS X 10_15_7" whatever the real macOS version.
- Chrome reports only the main version (the other numbers are zeros), and on Android it reports the device as "K" and the system as "Android 10" whatever the real model and version.
- iPad browsers often claim to be a Mac, to receive desktop pages.
Chromium browsers now offer the missing details separately, as "client hints", and only to sites that ask.
Why you might need yours
- Reporting a problem to a website's support team. Copy the line from the box and paste it into your message.
- Checking which version you are running without opening menus.
- Web development: seeing what a server receives from a device.
- Understanding a log entry: paste a line from a server log to see what kind of visitor it was.
Can it be changed?
Yes. The "request desktop site" option in mobile browsers works by sending a desktop user agent. Developer tools in every desktop browser can pretend to be any device. Because the line is so easy to change, websites must never treat it as proof of anything; it is a polite label, not an identity.
Is my user agent personal information?
Not by itself: millions of people share the same line. It becomes identifying only in combination with other details and your IP address.
Why does every browser say "Mozilla"?
In the 1990s some sites sent their best pages only to Netscape, whose code name was Mozilla. Other browsers began claiming to be Mozilla to get the same pages, and the word stuck.
Does incognito mode change the user agent?
No. A private window sends the same line as a normal one.