User-agent (UA) is software that acts on behalf of a user. Through the user agent, the website you visit will know information about the browser and operating system you are using.
According to Hal Science, user-agent fingerprinting is a technique used by websites and online services to gather information about a user’s web browser and operating system. The user-agent string, which is a text string that identifies the browser and operating system being used, is one of the primary attributes used in user-agent fingerprinting. Other attributes, such as the list of installed fonts or the presence of certain browser plugins, can also be used to identify a user’s system. A browser can figure out the following elements by accessing this string: operating system type, OS version, browser type, and browser core (version). On websites that test fingerprints, such as whoer.net and browserleaks.com, the user-agent value of a browser can be examined.