What is User Agent Parser?
The User-Agent (UA) string is an HTTP request header sent by every web browser, crawler, and HTTP client to identify itself to servers. It typically encodes the browser name and version, the rendering engine, the operating system and version, and device type (desktop, mobile, tablet). UA strings follow no strict standard and have accumulated decades of compatibility quirks — most modern browsers include "Mozilla/5.0" for historical reasons, and Chromium-based browsers include "Safari" in their UA to maximize compatibility. Parsing UA strings is used for analytics, bot detection, adaptive content delivery, and debugging browser-specific issues.