A browser's user agent string (UA) helps identify which browser is being used, what version, and on which operating system. When feature detection APIs are not available, use the UA to customize behavior or content to specific browser versions.
A user agent is a small piece of data sent by your web browser when accessing a website or application. It identifies the type of browser, device, operating system, and browser version. This information helps websites ensure optimal performance and compatibility, and allows developers to customize their sites based on user agent data.