Browser Compatibility Test Template

Check your analytics. Pull the last 90 days of browser and device data. Rank browsers by session count. Draw the line at 95% cumulative coverage for Tier 1. Browsers between 95-99% cumulative are Tier 2. Everything below 99% is Tier 3. Review quarterly because browser share shifts. Two years ago Edge Chromium was Tier 2 for most products. Today it is Tier 1 for many.

Run automated cross-browser tests on every PR for Tier 1 browsers. Run full manual browser sweeps before major releases (new features, redesigns, framework upgrades). Quick spot-checks are sufficient for minor releases that do not touch CSS or client-side JavaScript. The [smoke test template](/templates/smoke-test-template) helps define a minimal browser check that runs on every deployment.

Both. Use BrowserStack, Sauce Labs, or LambdaTest for automated cross-browser test execution in real browser environments. Use browser DevTools device emulation for quick layout checks during development. But always validate on at least one physical iOS device and one physical Android device before major releases. Emulators miss touch interaction nuances, hardware keyboard behavior, and performance differences.

IE 11 reached end of life in June 2022. Microsoft Edge is the replacement. Unless your analytics show significant IE traffic (some enterprise and government products still have IE users), do not test for IE. If you must support IE, use a separate compatibility layer with transpilation (Babel) and polyfills, and accept that some modern features will not work.

First, check if the issue is a genuine browser bug or a spec interpretation difference. MDN Web Docs and caniuse.com are the references. For genuine bugs, use CSS feature queries (`@supports`) to provide fallbacks. Avoid user-agent sniffing. Document accepted visual differences in the known issues tracker so QA does not re-file them every release. ---