User Agent

User agents are defined in the HTTP Header by user-agent strings, which often list the specific browser, with the version, as well as the device and/or host operating system that the browser will work on. User agents can also be bots and other software that emulate individual users. Google has published a list of their popular User Agent Strings for devices here: https://developer.chrome.com/multidevice/user-agent and a list of common GoogleBot User Agent Strings here: https://support.google.com/webmasters/answer/1061943?hl=en