Know the three measurements
Largest Contentful Paint (LCP) measures when the main content appears, Interaction to Next Paint (INP) reflects responsiveness to interactions, and Cumulative Layout Shift (CLS) measures unexpected visual movement. These metrics describe experience signals, not a shortcut or guarantee for ranking.
Use the right evidence
Field data reflects real eligible visitors over time; lab tools help reproduce and diagnose problems under test conditions. Compare templates and devices, because a homepage result may not represent a service page or checkout. Check the current thresholds in Google's documentation before interpreting a score.
See Google's current Core Web Vitals guidance.
Fix the cause, then retest
Large images, render-blocking scripts, heavy third-party widgets and late-loading fonts are common investigation points. Reserve image dimensions, load only what a page needs and test changes against both performance and usability. Retest real page templates after deployment; a single score is not a complete quality assessment.