A user agent is a string of text that identifies the browser and operating system to the web server you are connecting to.
When you connect to a website, you are sending your User-Agent in a field in your HTTP header. The content of the user agent vary from browsers and operating systems. The web server can use this information to serve different web pages or just collect visitor information for analytics. A User Agent can also be used in analytics and statistics showing the browsers and operating systems in use by their visitors.
User Agent Lookup: