User-Agent Parser
Parse and analyze browser user-agent strings to detect device and OS.
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/149.0.0.0 Safari/537.36The User Agent is a string sent by the browser with every HTTP request. It identifies the browser, operating system, and device of the user.
This tool parses the string locally in the browser using regular expressions to detect known patterns of browsers, operating systems, and devices.
What's actually inside a user-agent string — and how to read it
A user-agent string encodes browser name, version, rendering engine, OS, device type, and sometimes hardware details — all in a single unstructured header your server receives with every HTTP request.
The string 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36' identifies Chrome 124 on Windows 11 64-bit. The leading 'Mozilla/5.0' is a legacy compatibility token that all browsers still include. AppleWebKit is the engine, Chrome/124 is the actual browser. Parsing this correctly requires pattern matching against known browser signatures.
Identifying crawler and bot user agents before they hit your server
Googlebot, Bingbot, and other search engine crawlers identify themselves in the user-agent string. Parsing these correctly lets you serve different content to crawlers, block malicious scrapers, or analyze how bots interact with your site.
A bot user-agent typically contains keywords like 'bot', 'crawl', 'spider', or 'slurp'. Googlebot's UA includes 'Googlebot/2.1'. Malicious scrapers sometimes spoof legitimate browser UAs — which is why bot detection should be supplemented with behavioral analysis, not just UA matching. Use this tool to test UA strings from your access logs to identify which requests came from actual browsers versus automated clients.
Using user-agent parsing to diagnose device-specific rendering bugs
When a bug only affects certain browsers or mobile devices, parsing the user-agent from your error logs tells you exactly which browser version and OS combination is causing the issue.
Your analytics show 40% mobile traffic but your design team says it looks fine on their iPhone. The device type in the user-agent tells you browser, OS version, and device category — so you can reproduce the exact environment. Safari on iOS 16 behaves differently from Chrome on Android 14. Paste a UA from your error logs here to immediately identify the browser and OS without running device-specific testing.
Parsing user-agents in server logs and API access records
Server access logs record the user-agent string for every request. Parsing these strings lets you segment traffic by browser, OS, and device type for analytics, capacity planning, and bot filtering.
If you're building middleware that adapts responses based on client capabilities, or writing a bot filter that blocks scrapers but allows search engines, accurate user-agent parsing is the foundation. This tool handles the parsing logic client-side — paste any UA string from your logs, nginx access files, or API request records to decode it instantly.