User Agent
The identifying string a browser sends with every request, telling the server which browser, version, and operating system is making the request.
Full Definition
The User-Agent HTTP header is a string that identifies the client making the HTTP request — its browser name and version, rendering engine, and operating system. Real browsers send strings like "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/125.0.0.0 Safari/537.36". Default user agents in scraping libraries often expose themselves: Python's requests sends "python-requests/2.x.x" by default. Always setting a realistic, up-to-date browser user agent is a basic but essential step in avoiding bot detection. User agent alone is insufficient — it must match the rest of the request fingerprint.
