Lesson 18 / 25
WebPageTest and real-world testing
Test performance across real browsers, devices, and network conditions using WebPageTest.
WebPageTest setup and analysis
Visit webpagetest.org, enter URL, select location/browser/network. Results show waterfall charts, filmstrip view, metrics. Test on slow networks (3G) and older devices. Compare variations A/B to quantify improvements.
Real User Monitoring (RUM)
Collect performance data from real users with RUM services (Google Analytics, New Relic, Datadog). Measure Core Web Vitals across browsers, devices, networks. Compare synthetic vs real-user data—they often differ significantly.
Real-world testing best practices
Test on actual slow networks and old devices. DevTools throttling doesn't perfectly simulate reality. Use RUM for baseline metrics. Synthetic tests find regressions, RUM finds real impacts. Correlate performance with business metrics.
Quick check
Quick check: What is RUM (Real User Monitoring)?
- Measuring performance from actual user devices
- Laboratory testing only
- Testing with Rum, a beverage