Free Online User Agent Parser: Decode Browser Strings Instantly
A user agent string is technical data your web browser transmits with every HTTP request. This identifier reveals your browser type, version number, operating system, device architecture, and rendering engine to web servers.
Unlike generic identifiers, user agent strings follow a specific format defined by RFC 7231 standards. Web developers rely on parsing these strings for cross-browser compatibility testing, responsive design implementation, and analytics tracking. Our parser extracts browser name, version, OS details, and device type from any valid user agent string.
How User Agent Detection Works in Web Browsers
Browser Fingerprinting via User-Agent Header
The User-Agent HTTP header identifies browser type (Chrome, Firefox, Safari), version numbers, and rendering engine (Blink, Gecko, WebKit). Servers parse this data to deliver compatible HTML, CSS, and JavaScript code that matches your browser's capabilities.
Mobile vs Desktop User Agent Detection
Device classification happens through keywords like "Mobile", "Android", "iPhone", or "iPad" in the UA string. This triggers responsive design systems to serve touch-optimized interfaces for smartphones and tablets versus mouse-driven layouts for desktops.
User Agent String Structure: Breaking Down Browser Identifiers
Modern user agent strings contain multiple data points separated by specific delimiters. Understanding each component helps developers implement accurate browser detection scripts and device recognition algorithms.
Product Token (Browser Name)
Identifies the browser: Chrome/120.0, Firefox/117.0, Safari/16.6
Platform Details (OS Information)
Operating system and architecture: Windows NT 10.0; Win64; x64 or Macintosh; Intel Mac OS X 10_15_7
Engine Identifier (Rendering Engine)
Layout engine version: AppleWebKit/537.36, Gecko/20100101
Compatibility Tokens (Legacy Support)
Historical markers: Mozilla/5.0, KHTML, like Gecko for backwards compatibility
Why Parse User Agent Strings? Real-World Applications
Cross-Browser Testing Automation
QA teams parse UA strings to verify cross-browser compatibility across Chrome, Firefox, Safari, and Edge versions. Automated testing frameworks like Selenium use UA detection to route tests to specific browser configurations.
Web Analytics & Traffic Analysis
Analytics platforms extract browser and OS data from user agents to generate visitor demographics reports. Marketing teams leverage this intel to prioritize browser support and optimize campaigns based on actual user technology stacks.
Bot Detection & Security Filtering
Security systems analyze UA patterns to distinguish legitimate traffic from automated bots, scrapers, and malicious crawlers. Anomalous or spoofed user agents trigger additional verification steps like CAPTCHA challenges.
Adaptive Content Delivery via CDN
Content delivery networks parse user agents server-side to serve device-optimized assets—WebP images for modern browsers, JPEG fallbacks for older ones, and compressed mobile variants for smartphones detected via UA mobile keywords.
Progressive Enhancement Strategies
Frontend developers implement feature detection by checking UA strings for specific browser capabilities. While modern APIs like navigator.userAgentData replace some use cases, UA parsing remains critical for legacy browser support.
User Agent String Examples by Browser and Platform
Below are actual user agent strings from popular browsers. Notice how each contains platform info, browser version, and engine details formatted per HTTP specification standards.
Google Chrome 120 on Windows 11 (64-bit)
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36Indicates Blink engine, Windows NT 10.0 (Windows 11), x64 architecture
Mozilla Firefox 117 on Ubuntu Linux
Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/117.0Uses Gecko rendering engine, X11 display server, Linux x86_64 platform
Safari 17 on iPhone (iOS 17)
Mozilla/5.0 (iPhone; CPU iPhone OS 17_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.0 Mobile/15E148 Safari/604.1Mobile identifier present, WebKit engine, iOS version encoded as 17_0
Microsoft Edge 119 on macOS
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/119.0.0.0 Safari/537.36 Edg/119.0.0.0Chromium-based Edge, includes "Edg" token, macOS 10.15.7 (Catalina)
User Agent Parser FAQ: Common Questions Answered
How do I change my browser's user agent string?
Modern browsers let you modify UA strings via developer tools (F12 → Network Conditions → User Agent). Browser extensions like "User-Agent Switcher" provide GUI controls. Developers use this technique called user agent spoofing to test mobile layouts on desktop or simulate different browser versions during QA testing.
Can websites detect if I spoofed my user agent?
Yes. Advanced fingerprinting compares the UA string against actual browser capabilities detected through JavaScript APIs. If your UA claims to be Safari but supports Chrome-exclusive features, detection systems flag the mismatch. The new User-Agent Client Hints API makes spoofing harder.
Why do Chrome user agents contain "Safari" and "Mozilla"?
Browser history explains this quirk. Early websites checked for "Mozilla" to detect Netscape. When other browsers emerged, they added "Mozilla" for compatibility. Chrome includes "Safari" because it's based on WebKit (Safari's engine). These compatibility tokens prevent legacy sites from blocking modern browsers they don't recognize.
What user agent strings do search engine crawlers use?
Google uses multiple UAs including Googlebot/2.1 for web crawling and Googlebot-Image for image indexing. Bing employs bingbot. Webmasters check robots.txt files to verify bot identity and control crawler access to site sections.
Is user agent sniffing better than feature detection?
No. Modern web development prioritizes feature detection (checking if APIs exist) over UA parsing because browsers can lie about their identity. However, UA sniffing remains useful for analytics, bot detection, and serving mobile-specific content when feature detection isn't practical. Combine both approaches for robust cross-browser support.
Related Web Development Tools
How to Access User Agent Data: Code Examples
Developers can extract user agent information through multiple methods depending on whether you're working server-side or client-side.
Server-Side Detection (HTTP Headers)
app.get('/api/detect', (req, res) =62 123 const ua = req.headers['user-agent']; console.log(ua); 125);$userAgent = $_SERVER['HTTP_USER_AGENT']; echo $userAgent;Server-side parsing happens before page rendering, enabling conditional content delivery based on device type.
Client-Side Detection (JavaScript)
const ua = navigator.userAgent; const isMobile = /Mobile|Android|iPhone/i.test(ua);navigator.userAgentData?.getHighEntropyValues( ['platform', 'platformVersion'] ).then(data =62 console.log(data));JavaScript detection allows dynamic UI adjustments after page load without server requests.
HTTP Request Example with User-Agent Header
GET /api/data HTTP/1.1 Host: example.com User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate, br Connection: keep-aliveEvery HTTP request automatically includes the User-Agent header, making it available to web servers for processing.
Start Parsing User Agent Strings Now
Free online tool with instant results. No registration, no limits. Perfect for developers, QA testers, and system administrators.