User Agent
A User-Agent (UA) is a standard HTTP request header sent by a browser or client application to a web server. It communicates the client's browser software, engine version, operating system, and hardware architecture, allowing servers to format responses and evaluate request legitimacy.
When a browser initiates an HTTP request, it transmits its identity via the User-Agent header. Default HTTP client libraries (such as Python requests or urllib) send explicit script headers (e.g., python-requests/2.31.0), which Web Application Firewalls (WAFs) identify and block immediately.
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.0.0 Safari/537.36
String Anatomy Breakdown
Mozilla/5.0: Legacy platform compatibility token present in almost all modern browser UAs.(Windows NT 10.0; Win64; x64): Operating system (Windows 10/11) and CPU architecture (64-bit).AppleWebKit/537.36: Underlying HTML layout engine (WebKit fork used by Blink).Chrome/127.0.0.0: Browser application name and major build version number.Safari/537.36: WebKit rendering compliance indicator.
Modern User-Agent Reference List
When selecting a user agent for web scraping, use active browser strings. Outdated strings trigger instant anti-bot inspection rules.
# Desktop Chrome 127 (Windows 11)
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.0.0 Safari/537.36
# Desktop Chrome 127 (macOS Sonoma)
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.0.0 Safari/537.36
# Desktop Firefox 128 (Windows 11)
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:128.0) Gecko/20100101 Firefox/128.0
# Mobile Safari (iPhone iOS 17.5)
Mozilla/5.0 (iPhone; CPU iPhone OS 17_5_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.5 Mobile/15E148 Safari/605.1.15
# Mobile Chrome (Android 14)
Mozilla/5.0 (Linux; Android 14; SM-S928B) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.6533.103 Mobile Safari/537.36
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