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, your browser sends a user agent string to the web server. 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.

For example, a user agent string might look like this:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3