The user agent (UA) is a string sent in HTTP request headers that identifies the client software — browser type, version, and operating system. Websites use it to serve the right content format and as a basic bot-detection signal.
Scrapers that send default HTTP library user agents (like "python-requests/2.28") are trivially detectable. Rotating realistic UA strings matching current browser versions and their exact header ordering is a baseline anti-bot countermeasure. Full browser fingerprinting goes beyond UA to include screen resolution, fonts, WebGL renderer, timing data, and hundreds of other signals — making a convincing browser impersonation significantly harder than swapping a header string.