Website Performance: Core Web Vitals and Mobile Journeys

Measure the experience people receive

Core Web Vitals cover loading, responsiveness and visual stability. The good-experience thresholds are LCP at or below 2.5 seconds, INP at or below 200 milliseconds and CLS at or below 0.1, assessed at the 75th percentile. These thresholds come from Web Vitals guidance.

Find the largest sources of work

Check the main image, render-blocking resources, unnecessary JavaScript, font loading and third-party scripts. Send appropriately sized images, reserve media dimensions and lazy-load images below the initial view. Avoid making a phone generate decorative images at runtime when a static asset gives the same result.

Split article bodies and large datasets away from shared application code. Defer features that are not needed to understand the offer or complete the principal task. Every script should have an identifiable purpose.

Test more than the homepage

Review a commercial page, an article and the contact journey on narrow screens. Open menus, follow CTAs and submit a form. Check that content remains visible and usable when motion is reduced.

Report measurements honestly

A local or Lighthouse result is a lab measurement under specific conditions. Field data reflects actual users over time and may be unavailable for a small site. Record the device, network, route and test version; compare like-for-like runs. A score is a diagnostic aid, not a guarantee of conversions or rankings.

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