What is a user agent string?

A user agent string is a line of text a browser sends with every web request, identifying the browser, its version, the rendering engine, and the operating system it's running on.

Is my user agent string uploaded anywhere?

No. Parsing happens entirely in your browser using JavaScript — the string you paste or your own browser's UA is never sent to a server.

Why does the parser show Unknown for some fields?

Some user agent strings omit details like device vendor or model, especially on desktop browsers, or they may be malformed or heavily trimmed by privacy features.

Can a user agent string be faked?

Yes. Any browser or script can send an arbitrary user agent string, so UA parsing should never be used alone for security decisions — it's best for analytics, debugging, and compatibility checks.

What's the difference between the browser and the rendering engine?

The browser is the application itself, like Chrome or Firefox, while the rendering engine, like Blink or Gecko, is the underlying software that renders web pages — several browsers can share the same engine.

Why does my browser report an old browser name in its UA?

For compatibility, many browsers still include legacy tokens like Mozilla/5.0 or old version numbers rooted in decades-old standards — this is historical baggage, not a sign that you're running outdated software.