What a User-Agent is
It's a string sent by the browser on every HTTP request, identifying the browser, its version, the operating system, and sometimes the device type. Servers and analytics use this to adapt content or collect statistics.
How to use it
The field is pre-filled with your own browser's User-Agent — but you can paste any other string (from a server log, for example) to identify it.
Heuristic identification
Identification is based on known patterns in the most common User-Agents — it's not 100% guaranteed for very unusual or custom strings, since there's no strict official standard for the User-Agent format.
Frequently asked questions
Why is the field already filled in?
For convenience, it's auto-filled with your own browser's User-Agent (the same information it already sends to every site you visit).
Is the identification always 100% accurate?
No — it's based on common patterns found in most real User-Agents. Very rare or spoofed strings may not be identified correctly.