A User-Agent string is a short text string that your browser includes in the HTTP request headers every time you visit a website. It identifies your browser (Chrome, Firefox, Safari), its version, and your operating system. Servers use it to serve device-appropriate content.
Example User-Agent Strings
| Browser | User-Agent Example |
|---|---|
| Chrome on Windows | Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36 |
| Safari on iPhone | 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/604.1 |
| Firefox on macOS | Mozilla/5.0 (Macintosh; Intel Mac OS X 14.0; rv:122.0) Gecko/20100101 Firefox/122.0 |
How User-Agents Are Used
- Responsive design: Servers detect mobile vs desktop to serve appropriate versions.
- Browser compatibility: Legacy servers serve browser-specific CSS or JavaScript.
- Analytics: Websites track which browsers and OSes their visitors use.
- Bot detection: Security systems compare User-Agent against expected patterns to detect scrapers.
- Fingerprinting: Combined with other browser attributes, contributes to device fingerprinting.
Privacy and User-Agents
Your User-Agent reveals your browser and OS version. While this alone is not identifying, combined with other data points it contributes to browser fingerprinting. Modern privacy browsers like Brave randomize or standardize User-Agents to reduce this.
People Also Ask
- Can I change my User-Agent?
- Yes. Browsers like Chrome have a Developer Tools override (Network conditions pane). Browser extensions like "User-Agent Switcher" also let you set any User-Agent, though advanced fingerprinting can detect mismatches between your User-Agent and actual browser behavior.
Related: Browser fingerprinting | Browser data leaks | Fingerprint Check