What Is a User Agent?
A user agent is a small piece of data sent by your web browser when accessing a website or application. It identifies the type of browser, device, operating system, and browser version. This information helps websites ensure optimal performance and compatibility, and allows developers to customize their sites based on user agent data.
A browser's user agent string (UA) helps identify which browser is being used, what version, and on which operating system. When feature detection APIs are not available, use the UA to customize behavior or content to specific browser versions.
Common uses of user agent analysis:
- User experience testing: Verify how websites render across different viewports and layout engines to maintain high-quality designs.
- Browser compatibility testing: Ensure scripts and styles execute correctly across various legacy and modern browser versions.
- Website personalization tools: Tailor content, language settings, and interface components based on the client's detected OS or device.
- Browser security software: Cross-reference user agents to audit outdated software versions and identify malicious crawler bots.