A user agent is a string that identifies the client application (such as a web browser, bot, or other software) to the web server. It is often used to tailor content for different devices or applications. Common types of user agents include web browsers (e.g., Chrome, Firefox, Safari), bots (e.g., Googlebot, Bingbot), and mobile devices (e.g., Android, iPhone).
User agents play a vital role in web scraping, where impersonating specific browsers or devices can help bypass restrictions and avoid detection. They enable websites to deliver optimized experiences by detecting the device or application accessing the site. For example, a web server may serve a simplified page for a mobile user agent like Mozilla/5.0 (Linux; Android 10) while delivering a full version for a desktop user agent such as Mozilla/5.0 (Windows NT 10.0; Win64; x64).