A user agent is a string of text that your browser automatically sends to every website you visit. It identifies your browser, its version, and your operating system β giving websites the information they need to serve compatible content. You can see your current user agent string on whatsmy.fyi.
What Does a User Agent Look Like?
A typical user agent string for Chrome on Windows looks like this:
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36That string contains several pieces of information:
- Mozilla/5.0 β a legacy token present in virtually all modern browser user agents for historical compatibility reasons.
- Windows NT 10.0; Win64; x64 β the operating system (Windows 10/11, 64-bit).
- AppleWebKit/537.36 β the rendering engine (Blink, which descends from WebKit).
- Chrome/124.0.0.0 β the browser name and version.
- Safari/537.36 β another legacy compatibility token.
Why Is the User Agent So Confusing?
User agent strings look messy because of decades of browser wars. In the 1990s, web servers served different content to different browsers. Netscape was dominant, so other browsers began identifying themselves as "Mozilla" to get the good content. Internet Explorer, then Opera, then Chrome and Safari β all adopted the convention of including "Mozilla/5.0" regardless of their actual identity. The tradition stuck, making raw user agent strings difficult to parse by eye.
What Information Does Your User Agent Reveal?
Your user agent tells websites:
- Your browser name (Chrome, Firefox, Safari, Edge, etc.)
- Your browser version number
- Your operating system (Windows, macOS, Linux, iOS, Android)
- Your OS version
- Whether you are on a mobile or desktop device
- The underlying rendering engine (Blink, WebKit, Gecko)
User Agents and Browser Fingerprinting
Your user agent is one component of a broader technique called browser fingerprinting. By combining your user agent with other signals β your IP address, screen resolution, installed fonts, timezone, and language preferences β websites can create a unique "fingerprint" of your browser that can track you across sites without cookies.
Browser fingerprinting is harder to block than cookies. Even if you clear cookies or use private browsing, your browser fingerprint remains the same as long as your browser configuration does not change.
Check your privacy score on whatsmy.fyi to see how unique your browser fingerprint is.
How Do Websites Use Your User Agent?
- Content negotiation: Serving mobile-optimised pages to phones and desktop pages to laptops (though CSS media queries have largely replaced this).
- Feature detection: Checking whether your browser supports specific HTML5 or CSS features.
- Analytics: Tracking which browsers and operating systems their visitors use.
- Bot detection: Unusual or missing user agents are a signal that a visitor may be a web scraper or bot.
Can You Change or Fake Your User Agent?
Yes. All major browsers include developer tools that let you change your user agent. Extensions like "User-Agent Switcher" make it easy to spoof any browser or device. However, changing your user agent alone does not guarantee anonymity β websites can detect inconsistencies between your user agent and other browser capabilities.
Frequently Asked Questions
Does my user agent reveal my IP address?
No. The user agent is sent in an HTTP header, but your IP address is a separate piece of network-layer information. They are independent.
Can I remove my user agent entirely?
Technically yes, but sending no user agent or an empty user agent will cause many websites to break or serve incorrect content. Some sites also block requests with missing user agents as a bot-prevention measure.
Is the user agent the same thing as the browser version?
The user agent includes the browser version as one of its components, but it also contains much more: the OS, rendering engine, and device type. Parsed correctly, whatsmy.fyi extracts just the browser name and version for the Browser & OS card.
