The User-Agent plays a crucial role in anti-crawler mechanisms by acting as an identifier for the client making HTTP requests. It is a header field that provides information about the browser, operating system, and device type used by the requester. Websites can analyze the User-Agent string to distinguish between legitimate users and automated bots.
For example, if a website detects a User-Agent like "Python-urllib/3.10" or "Scrapy/2.6.1," it may block the request since these are commonly used by web crawlers. Conversely, a standard browser User-Agent like "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/117.0.0.0 Safari/537.36" is more likely to be treated as a legitimate user.
In anti-crawler strategies, websites may maintain a whitelist of trusted User-Agents or flag suspicious ones for further verification, such as CAPTCHA challenges.
To enhance anti-crawler defenses, Tencent Cloud offers services like Tencent Cloud Web Application Firewall (WAF), which can detect and block malicious crawlers based on User-Agent analysis, IP reputation, and behavioral patterns. Additionally, Tencent Cloud Anti-DDoS helps mitigate large-scale scraping attempts by filtering abnormal traffic.