FernTool

What is a user agent?

A user agent is the software acting for you on the web, usually your browser. With every request it sends a User-Agent header describing itself. See yours on the what is my user agent page.

Reading a user agent string

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36
(KHTML, like Gecko) Chrome/129.0.0.0 Safari/537.36

Why does every browser claim to be Mozilla?

In the 1990s, sites served advanced pages only to Netscape, whose code name was Mozilla. Internet Explorer started saying “Mozilla compatible” to get the good pages, and every browser since has copied the trick. The result is strings that mention three or four browsers at once.

How websites use it

To choose mobile or desktop layouts, offer the right app download, work around browser bugs, block outdated browsers and produce browser statistics. Search engines identify their crawlers this way too, for example Googlebot and bingbot, though anyone can fake a user agent, so serious sites verify bots by IP and reverse DNS.

User-Agent reduction and Client Hints

Detailed strings help trackers fingerprint you, so Chromium browsers now freeze the OS version and minor version numbers. Sites that need details request them via User-Agent Client Hints (Sec-CH-UA headers).

How to change your user agent

In Chrome or Edge: DevTools (F12) → ⋮ → More tools → Network conditions → untick “Use browser default”. In Firefox: set general.useragent.override in about:config. On the command line: curl -A "MyAgent/1.0" https://www.ferntool.com/api/user-agent. Changing it doesn’t hide your IP address.

Frequently asked questions

Is a user agent personal information?

Not by itself, since millions share the same string, but it contributes to browser fingerprinting when combined with other details.

What is my user agent?

Open FernTool’s user agent page to see your exact string, browser, version and operating system.

Can websites see my user agent?

Yes. Every site you visit receives it automatically with each request.

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