Paste a User-Agent string (your own is pre-filled) and the tool detects the browser and version, OS, device category and layout engine in a summary table.
For historical compatibility most browsers include tokens like Mozilla, AppleWebKit and Safari, so detection relies on the most specific marker.
It infers Mobile, Tablet or Desktop from known tokens, but heavily customized or spoofed UA strings may report as Unknown.
It is a useful hint, not a guarantee — UA strings can be spoofed or frozen, so treat the result as best-effort detection.