User Agent Parser

Parse user agent strings to identify browser, operating system, device type, and rendering engine. Detect bots and crawlers.

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What is a user agent string?

A user agent string is a text identifier that browsers and other HTTP clients send with every request. It tells the server what software is making the request, including the browser, operating system, and device.

A typical user agent looks like:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

Why user agents are complex

User agents are notoriously messy due to decades of browser history. Most browsers claim to be “Mozilla” and “Safari” for compatibility, even when they’re neither.

Chrome’s 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

It claims to be Mozilla, WebKit, Gecko, Chrome, AND Safari - all for historical compatibility reasons.

Parsing user agent components

Browser detection order matters - Check specific browsers before generic ones:

  1. Edge (contains “Chrome” too)
  2. Opera (contains “Chrome” too)
  3. Chrome
  4. Safari
  5. Firefox

Operating system patterns:

  • Windows NT 10.0 = Windows 10 or 11
  • Mac OS X = macOS
  • Linux = Linux
  • Android = Android
  • iPhone OS = iOS

Device type indicators:

  • Mobile = Phone
  • Tablet = Tablet
  • TV = Smart TV

Detecting bots and crawlers

Major search engine bots identify themselves:

Googlebot/2.1 (+http://www.google.com/bot.html)
bingbot/2.0 (+http://www.bing.com/bingbot.htm)

Social media crawlers:

facebookexternalhit/1.1
Twitterbot/1.0
LinkedInBot/1.0

Command-line tools:

curl/7.68.0
wget/1.20.3
python-requests/2.25.1

User agent in different contexts

Server-side - For content negotiation, analytics, bot detection:

user_agent = request.headers.get('User-Agent')
if 'bot' in user_agent.lower():
    serve_static_html()

Client-side - For feature detection (though feature detection is preferred):

// Not recommended - use feature detection instead
const isChrome = navigator.userAgent.includes('Chrome');

// Better approach
const hasTouch = 'ontouchstart' in window;

Client hints: the modern alternative

Client Hints provide structured device information without the messy user agent string:

Sec-CH-UA: "Chrome";v="120", "Chromium";v="120"
Sec-CH-UA-Mobile: ?0
Sec-CH-UA-Platform: "Windows"

Benefits:

  • Structured, easy to parse
  • Opt-in (privacy friendly)
  • Reduces fingerprinting surface

Common user agent use cases

Analytics - Track browser and OS usage.

Content adaptation - Serve mobile-specific content.

Bot management - Allow/block specific crawlers.

Compatibility - Serve polyfills for older browsers.

A/B testing - Target specific browser versions.

How this tool works

This tool parses your browser’s user agent (or a custom string you provide) and extracts browser, OS, device, and engine information. It also detects bots and crawlers. Powered by a QuantCDN Edge Function.