pagespeed-insights

Improving a PageSpeed Insights score starts with fixing Core Web Vitals: optimize the LCP element, prevent layout shifts with explicit dimensions, and defer render-blocking CSS and JavaScript. Re-test after each change and target scores of 90 or higher.

Good Core Web Vitals thresholds are LCP under 2.5 seconds, CLS under 0.1, and INP under 200 milliseconds, measured at the 75th percentile. FCP should be under 1.8 seconds and TTFB under 800 milliseconds.

Lab data is collected in a controlled Lighthouse environment and is useful for debugging, while field data comes from the Chrome User Experience Report and reflects real user experiences. Both should be balanced when optimizing performance.

Fix CLS from images by setting explicit width and height attributes or using the CSS aspect-ratio property so the browser reserves space before loading. Also reserve space for ads and embeds and avoid inserting content above existing content.

Lighthouse lab data uses simulated conditions that may not capture real-world bottlenecks like slow networks or low-end devices. Check field data from CrUX, which aggregates actual user metrics over 28 days, to diagnose real-user performance.