What is a User-Agent string?+
A User-Agent (UA) string is sent by every browser in the HTTP request header. It identifies the browser, rendering engine, OS, and device type. Servers use it for analytics, device detection, and serving device-specific content.
Why do all browsers claim to be Mozilla?+
Browser UA strings include 'Mozilla/5.0' for historical compatibility reasons - web servers from the early internet served different content to non-Netscape browsers. Modern browsers kept the prefix to avoid being blocked by outdated server-side checks.
How do I change my User-Agent for testing?+
In Chrome DevTools: open DevTools → ... → More Tools → Network Conditions → uncheck 'Use browser default' and select or enter a custom UA string. This lets you test how your site behaves for different browsers or devices.
What is User-Agent Client Hints?+
UA Client Hints is the modern replacement for the UA string. Instead of one large string, browsers send structured headers (Sec-CH-UA, Sec-CH-UA-Platform) only sharing the data the server requests. It's more privacy-friendly and accurate.