Anatomy of the User-Agent String Structure

Even a User-Agent that looks complicated is made up of a few fixed pieces. Taking Chrome on desktop as an example:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36

The Meaning of Each Piece

• Mozilla/5.0 — a prefix left over from historical practice. Nearly every browser attaches it.
• (Windows NT 10.0; Win64; x64) — the platform token. Indicates the operating system and architecture.
• AppleWebKit/537.36 (KHTML, like Gecko) — the rendering engine family notation (shared by Blink/WebKit).
• Chrome/126.0.0.0 — the actual browser and version.
• Safari/537.36 — a Safari notation left in for compatibility.

How Is Mobile Different

A mobile UA adds a Mobile token, and the platform token includes the device model, as in Android 14; Pixel 8. iOS Safari uses unique tokens like iPhone; CPU iPhone OS 17_5 like Mac OS X and Mobile/15E148.

Notation of Derived Browsers

Edge, Opera, and Samsung Internet are Chromium-based, so they keep the Chrome/ token and append Edg/, OPR/, or SamsungBrowser/ at the end to distinguish themselves. So when parsing a UA, you need to check these derived tokens first to be accurate.

This site's reverse-parse preview breaks down the browser, engine, OS, and device according to the rules above.