Understanding User Agents
A User Agent (UA) is a string of text that your web browser sends to every website you visit. It identifies the browser application, operating system, vendor, and sometimes the device type (e.g., iPhone or Android).
Browser Fingerprinting
While UAs are necessary for websites to render the correct layout (Mobile vs Desktop), they are also used for tracking. The combination of your UA string, screen resolution, and installed fonts creates a unique "fingerprint" that can track you across the web without cookies.
Why spoof a User Agent?
Sometimes developers change (spoof) their UA string to test how a website responds to different devices. For example, you might set your desktop browser to send an "iPhone" user agent to see if the website loads the mobile version correctly.
Bot Detection
Search engines (like Googlebot) and scrapers identify themselves via the User Agent. System administrators use tools like this one to filter traffic logs and block malicious bots.