Question 1

What is a user agent string?

Accepted Answer

It is a text header your browser sends with every request, describing itself — roughly browser, version, engine, and operating system. Servers and scripts historically used it to adapt content, which is why it is full of legacy tokens like "Mozilla/5.0".

Question 2

Why does my user agent mention Mozilla, AppleWebKit, and Safari when I use Chrome?

Accepted Answer

For compatibility. Sites used to check for those tokens, so every new browser claimed them to avoid being served broken pages. A Chrome UA therefore contains Mozilla/5.0, AppleWebKit, and Safari plus its own Chrome token — parsers must check the most specific tokens first.

Question 3

What are client hints (userAgentData)?

Accepted Answer

A newer Chromium API that replaces UA sniffing with structured, privacy-conscious values: brand list, platform, and a mobile flag. Browsers are simultaneously freezing parts of the classic UA string (for example the Windows and macOS versions), so the UA alone is becoming less precise.

Question 4

Why can the parsed result be wrong or unknown?

Accepted Answer

User agents are self-declared and freely spoofable — browsers offer override switches and many bots imitate real browsers. Unusual apps, embedded WebViews, and brand-new browsers may also not match the parser's rules, in which case fields show as unknown.

Question 5

Is my user agent sent anywhere by this tool?

Accepted Answer

No. The string is read and parsed entirely inside your browser tab; nothing is uploaded or tracked. Note that your browser itself sends the user agent to every website you visit as a normal HTTP header — that is how the web works, not something this page adds.

User Agent Parser

Your user agent

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