User-Agent String Parser & Decoder
The HTTP User-Agent header is a string sent by your browser with every web request. It identifies the browser software, version, operating system, and rendering engine to the web server, allowing server-side adaptation of content.
User-Agent String Structure
A typical modern Chrome User-Agent looks like:
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36
Breaking this down: "Mozilla/5.0" is a historical compatibility token included by virtually all browsers. The platform token in parentheses contains the OS. "AppleWebKit/537.36" identifies the rendering engine. "Chrome/124.0.0.0" is the actual browser.
Detected Properties
- Browser & Version β Chrome, Firefox, Safari, Edge, Opera, Yandex Browser, etc.
- Operating System β Windows version, macOS version, Android version, iOS version, Linux distribution hint.
- Rendering Engine β Blink/WebKit (Chrome, Edge, Opera), Gecko (Firefox), WebKit (Safari).
- Device Type β Desktop, mobile phone, or tablet based on UA tokens.
- Bot Detection β Known crawler and bot signatures including Googlebot, Bingbot, curl, wget.
User-Agent and Privacy
Detailed User-Agent strings are a significant fingerprinting vector. The Chrome team is implementing User-Agent Client Hints (UA-CH) to gradually replace the detailed UA string with a more privacy-preserving API that requires explicit permission for detailed data.