User-Agent

The information contained within a User-Agent HTTP request header is also known as the User-Agent (UA) string. This string contains information on the device.

For example, if you browse the web on your smartphone, your device will send a HTTP request header to the web server, saying that it is a mobile device. The website will then respond and show you the mobile version of the page.

An example User-Agent string can be:

Mozilla/5.0 (Linux; Android 12; Pixel 6) AppleWebKit/537.36 (KHTML, like Gecko)
Chrome/93.0.4577.62 Mobile Safari/537.36

• Mozilla/5.0 - Largely ignored as has no relevance to the associated device
• Linux; Android 12 - details about the OS
• For mobile UA-strings, the "Pixel 6" section provides the device name or device model number
• AppleWebKit/537.6 - indicates what browser rendering engine is used. A rendering engine is what transforms HTML into a webpage on the screen
• KHTML, like Gecko - ensure compatibility for historical reasons
• Chrome/93.0.4577.62 Mobile Safari/537.36 - more detail on the browser and its version number.