Question 1

What is a User-Agent string?

Accepted Answer

A User-Agent (UA) string is text sent by browsers to servers identifying the browser, engine, OS, and device. Example: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

Question 2

Why do browsers start with Mozilla?

Accepted Answer

This is a historical quirk from the 'browser wars'. Netscape Navigator used 'Mozilla' in its UA, and servers would serve different content to Mozilla vs other browsers. Other browsers started with 'Mozilla' to get the same content.

Question 3

Can User-Agent strings be spoofed?

Accepted Answer

Yes, easily. Browsers and extensions can change the UA string. For critical decisions, use feature detection instead of UA parsing.

🔍 User-Agent Parser

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