Core Web Vitals

What is Core Web Vitals?

Core Web Vitals are three concrete metrics Google uses to gauge the perceived user experience of a page: LCP (Largest Contentful Paint) measures how fast the main content loads, INP (Interaction to Next Paint) measures how quickly the page responds to clicks and taps, and CLS (Cumulative Layout Shift) measures visual stability. INP replaced the earlier FID on March 12, 2024. A page passes when LCP is 2.5 seconds or less, INP is 200 ms or less, and CLS is 0.1 or less.

Why does Core Web Vitals matter?

For an online store the scores hit both the bottom line and visibility. Slow LCP and janky INP on product and collection pages increase drop-off and lower conversion exactly where the customer is closest to buying. Core Web Vitals also feed into Google’s page experience signals and can act as a tiebreaker between otherwise equally strong results. Google assesses the scores on field data from real visitors (the Chrome User Experience Report) at the 75th percentile, reported separately for mobile and desktop — so it is the slowest quarter of your users that decides the outcome.

Common use cases

• Diagnosing a slow product page with PageSpeed Insights or the Core Web Vitals report in Search Console.
• Optimizing LCP by compressing hero images, using WebP, and preloading the largest image.
• Removing CLS caused by banners, cookie popups, and fonts that shift the layout while the page loads.
• Improving INP by reducing heavy JavaScript from apps and third-party scripts.
• Documenting the impact of a new theme or app for developers or management.

Shopify perspective

Shopify themes often start out strong, but apps, chatbots, and tracking scripts typically drag the scores down. Always measure on real URLs with field data rather than a single lab number, and uninstall apps you no longer use. Rely on the theme’s native lazy loading and Shopify’s image CDN, and remember that popups and ad banners are the most common causes of poor CLS in practice.