What is a User Agent?

A user agent is a string that a web browser or other client software sends to a web server, identifying the type of device, operating system, and browser being used.

Here's an example of what a user agent looks like:

Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_12_0) AppleWebKit/535.38 (KHTML, like Gecko) Chrome/49.0.3532.306 Safari/537

If you'd like to see what your own user agent is, you can use a tool like WhatIsMyBrowser.

Combining user agent data with IP addresses

Combining user agent data with IP addresses enhances the ability to establish unique identifiers, especially in environments where cookies might be blocked or aren't being used at all.

While an IP address can give a rough location and possibly indicate shared use (like in a household or office), the user agent adds another layer of differentiation by identifying specific device and browser combinations.

For example, two users from the same IP address but with different user agents (indicating one is using a smartphone and the other a laptop) can be distinguished as separate visitors.