User Agent Parser
Parse and analyze user agent strings to extract browser, operating system, device type, and other information.
Paste a user agent string to parse its components. User agent strings identify the browser, operating system, and device making the request.
Table of Contents
What is a User Agent?
A user agent is a string that identifies the browser, operating system, and device making a request to a web server. It's sent as part of the HTTP headers in every web request and helps servers understand what kind of client is accessing their resources.
User agent strings were originally designed to help servers deliver content optimized for specific browsers or devices. However, they've evolved into complex strings that can reveal detailed information about the client environment.
The user agent string is accessible in JavaScript via navigator.userAgent and can be used for analytics, feature detection, and content adaptation.
User Agent Structure
User agent strings typically follow a pattern, though the exact format varies between browsers and devices. A common structure looks like this:
Product/Version (Platform Details) RenderingEngine/Version Browser/VersionExample user agent string:
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36Breaking this down:
Mozilla/5.0: Legacy identifier for compatibility(Windows NT 10.0; Win64; x64): Platform information (OS, architecture)AppleWebKit/537.36: Rendering engine and versionChrome/120.0.0.0: Browser name and versionSafari/537.36: Additional browser identifier
Components
Browser
The browser name and version (e.g., Chrome 120, Firefox 121, Safari 17). This helps servers determine which browser-specific features or workarounds to apply.
Operating System
The OS name and version (e.g., Windows 10, macOS 14, iOS 17). This information helps servers optimize content for different platforms and screen sizes.
Device Type
Whether the device is a Desktop, Mobile, or Tablet. This is crucial for responsive design and mobile optimization.
Rendering Engine
The underlying rendering engine (e.g., Blink, WebKit, Gecko). This helps identify compatibility and rendering capabilities.
Device Information
Specific device identifiers (e.g., iPhone, iPad, Android Phone). This can help with device-specific optimizations and analytics.
Common Use Cases
- Analytics: Track which browsers and devices visitors are using to make development decisions
- Feature Detection: Determine if a browser supports certain features before attempting to use them
- Content Adaptation: Serve different content or layouts based on device type (mobile vs desktop)
- Bug Tracking: Identify browser-specific issues by correlating errors with user agent strings
- Security: Detect suspicious or automated requests by analyzing user agent patterns
- A/B Testing: Segment users by browser or device for testing different features
Note: While user agent strings are useful, modern web development practices recommend using feature detection (via JavaScript APIs) rather than user agent sniffing when possible, as it's more reliable and future-proof.
Privacy Considerations
Fingerprinting
User agent strings can be used as part of browser fingerprinting, a technique that combines multiple pieces of information to uniquely identify users. This raises privacy concerns as it can track users across websites without cookies.
User Agent Spoofing
Many browsers and extensions allow users to modify or spoof their user agent string. This can be used for privacy protection, testing, or accessing content that's restricted to specific browsers.
Reduced User Agents
Some browsers are moving toward "reduced" or "minimal" user agent strings that reveal less information to protect user privacy. This is part of a broader effort to reduce fingerprinting capabilities.
Best Practices
When using user agent strings, only collect the minimum information necessary for your use case. Consider using feature detection instead of user agent parsing when possible, and be transparent about how you use this data.
Frequently Asked Questions
The "Mozilla" identifier is a legacy string that dates back to the early days of the web. It's included for historical compatibility reasons, even though modern browsers don't use the Mozilla rendering engine. Most browsers include it to ensure compatibility with older websites that check for this string.
User agent strings can be easily modified or spoofed by users or browser extensions. They should not be relied upon for security purposes. For feature detection, use JavaScript APIs instead. For analytics, user agent strings are generally reliable but should be used in combination with other signals.
The browser is the application the user interacts with (e.g., Chrome, Firefox, Safari). The rendering engine is the underlying software that renders web pages (e.g., Blink, Gecko, WebKit). Multiple browsers can share the same engine—for example, Chrome, Edge, and Opera all use the Blink engine.
Browsers that share the same rendering engine often have very similar user agent strings because they're built on the same underlying technology. For example, Chrome, Edge, and Opera all use Blink, so their user agent strings look similar. The browser name in the string helps distinguish them.
In JavaScript, you can access your user agent string using navigator.userAgent. You can also use the "Use My User Agent" button in this tool to automatically
populate the input field with your current browser's user agent string.
No. Modern best practices recommend using feature detection (checking if APIs exist)
rather than user agent parsing. For example, instead of checking if the browser is
Chrome, check if window.fetch exists. This is more reliable,
future-proof, and works even when users modify their user agent strings.
User agent reduction is an initiative by browser vendors to minimize the information revealed in user agent strings. This helps protect user privacy by reducing fingerprinting capabilities. Browsers are gradually moving to more generic user agent strings that reveal less specific information about the browser and OS versions.