Question 1

What is a User-Agent string?

Accepted Answer

A User-Agent string is a text identifier that web browsers and other applications send to web servers to identify themselves. It typically contains information about the browser name and version, operating system, device type, and rendering engine. This information helps websites deliver appropriate content and optimize the user experience for different platforms.

Question 2

How does the User-Agent Parser work?

Accepted Answer

This tool parses User-Agent strings entirely in your browser using the ua-parser-js library. Simply paste a User-Agent string or click "Use My User-Agent" to analyze your current browser. The parser extracts detailed information about the browser, operating system, device, rendering engine, and CPU architecture. All processing happens client-side - no data is sent to any server.

Question 3

Why do websites check User-Agent strings?

Accepted Answer

Websites use User-Agent strings for several purposes: (1) Serving mobile-optimized vs desktop layouts, (2) Detecting browser compatibility for specific features, (3) Analytics and usage tracking, (4) Security monitoring to detect bots and malicious traffic, (5) A/B testing across different platforms, and (6) Providing browser-specific workarounds or polyfills.

Question 4

Can User-Agent strings be spoofed?

Accepted Answer

Yes, User-Agent strings can be easily modified or spoofed. Browser extensions, developer tools, and custom HTTP clients allow users to send any User-Agent string they choose. This is why User-Agent detection should never be used as a security measure. Instead, websites should use feature detection (checking if specific APIs or capabilities exist) rather than relying on User-Agent strings for critical functionality.

Question 5

What is the difference between a bot User-Agent and a browser User-Agent?

Accepted Answer

Bot User-Agents typically identify themselves clearly (e.g., "Googlebot", "Bingbot") and include a URL for more information. They often have simpler structures without detailed browser/OS information. Browser User-Agents are more complex, containing rendering engine details, OS version, and device information. However, some malicious bots intentionally use browser-like User-Agents to avoid detection.

Question 6

How can I use this tool for security analysis?

Accepted Answer

Security teams can use this tool to: (1) Analyze User-Agents from web server logs to identify bot traffic, (2) Detect suspicious or malformed User-Agent strings that may indicate attacks, (3) Identify outdated browsers that may have known vulnerabilities, (4) Correlate attack patterns with specific browser versions or platforms, and (5) Validate that security tools and WAFs are correctly identifying clients.

Question 7

What are the different device types the parser can detect?

Accepted Answer

The parser can identify several device types: Desktop (traditional computers), Mobile (smartphones), Tablet (tablets and iPads), Wearable (smartwatches and fitness trackers), Console (gaming consoles like PlayStation or Xbox), and TV (smart TVs and streaming devices). If the device type cannot be determined from the User-Agent string, it defaults to "Desktop".

Question 8

How accurate is User-Agent parsing?

Accepted Answer

User-Agent parsing is generally accurate for well-formed, standard User-Agent strings from major browsers and known bots. However, accuracy can vary because: (1) User-Agents can be spoofed, (2) Some browsers intentionally provide misleading information for compatibility, (3) New browsers or versions may not be immediately recognized, (4) Custom applications may use non-standard formats. Always combine User-Agent detection with other techniques like feature detection.

User-Agent Parser

Example User-Agents

Desktop Browsers

Mobile Browsers

Bots & Crawlers

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