Parse a user agent string
Common user agents — click to parse
What is a user agent?
A user agent string is sent by every browser in the HTTP
User-Agent header. It tells the server what browser, OS, and device is making the request. Servers use it for analytics, feature detection, and serving different content to different clients.The Mozilla/5.0 mystery
Almost every browser starts with
Mozilla/5.0 — even Chrome, Safari, and Edge. This is a legacy quirk from the browser wars. Sites used to serve different content to Netscape (Mozilla) vs IE, so all browsers pretended to be Mozilla to get the best content.UA sniffing vs feature detection
Parsing user agents is unreliable — UAs can be spoofed and browsers frequently update. For production code, prefer feature detection (
if ('geolocation' in navigator)) over UA sniffing. Use UA parsing for analytics and logging, not for branching logic.UA reduction (Privacy)
Chrome and Edge are progressively reducing UA string detail as part of the Privacy Sandbox initiative. The new
User-Agent Client Hints API (navigator.userAgentData) is the modern replacement — structured, opt-in, and privacy-preserving.