User-Agent Parser

You are staring at an nginx access log, or chasing a bug that only happens on one customer's phone, and what you have is a long line starting with Mozilla/5.0. Paste the string here (or click the button to use your own) and it turns into four cards: browser and version, operating system, device type and rendering engine, plus tags flagging mobile devices, bots and programmatic access from curl, wget and friends.

User-Agents lie for historical reasons: every browser announces itself as Mozilla/5.0, Chrome carries Safari in its string and Edge carries Chrome. The parser (the ua-parser-js library) untangles this by token order and combination, not by naive substring search. Two version gotchas: Windows 11 still identifies itself as Windows NT 10.0, and macOS froze at 10_15_7, so the version you see can be older than the real one.

For log analysis, treat the tags as hints, not proof: bot detection is keyword-based (bot, crawler, spider), so a scraper masquerading as Chrome sails right through. A User-Agent is a claim made by the client, not an identity. Parsing happens in your browser and the string is never sent to a server (the library loads from a CDN). The built-in samples are handy for comparing desktop, iPhone and Googlebot formats.