Understanding Google's Core Web Vitals is crucial to driving SEO success for your brand.
Core Web Vitals are a set of essential metrics defined by Google to evaluate how users experience the loading, interactivity and visual stability of web pages. There are three core metrics:
- Largest Contentful Paint (LCP) — measures loading performance; how quickly the largest visible content element renders
- Interaction to Next Paint (INP) — measures responsiveness; how quickly the page responds to user interactions throughout the entire visit (replaced First Input Delay in March 2024)
- Cumulative Layout Shift (CLS) — measures visual stability; how much the page layout shifts unexpectedly as it loads
By understanding each metric, website owners can pinpoint areas for improvement and ensure their pages deliver a seamless user experience — which directly impacts search rankings.
Practical Tips for Optimisation
Improving LCP: Optimise images (compress and serve in modern formats like WebP or AVIF), use a CDN to reduce latency, leverage browser caching, and ensure your server responds quickly. The LCP element is often a hero image or heading — prioritise loading it above the fold without delay.
Improving INP: Minimise JavaScript execution time, break up long tasks, defer non-critical scripts, and avoid excessive DOM size. INP captures responsiveness across the full user session, so interactions like clicking buttons, opening menus and submitting forms all contribute.
Improving CLS: Set explicit width and height attributes on images and videos so the browser reserves space before they load. Avoid inserting content above existing content dynamically. Ensure web fonts don't cause layout shifts using font-display: optional or preloading critical fonts.
Tools you can use to measure and monitor your Core Web Vitals:
- Google PageSpeed Insights — lab and field data combined
- Google Search Console — real-user CWV data segmented by page type
- Lighthouse — detailed per-metric diagnostics
- Web Vitals Chrome Extension — real-time monitoring as you browse
How to Measure Each Metric
Knowing your scores is the starting point for improvement. Here is the recommended toolset for each metric:
LCP (Largest Contentful Paint)
- PageSpeed Insights — provides both lab-based LCP scores and field data from the Chrome User Experience Report (CrUX). The field data reflects real-user load times across your actual traffic, which is what Google uses for ranking. A good LCP score is under 2.5 seconds; above 4 seconds is classed as poor.
- Google Search Console (Core Web Vitals report) — shows LCP status aggregated by URL group, letting you quickly identify whether mobile or desktop has more failing pages. Use this to prioritise which page templates to fix first rather than optimising page-by-page.
INP (Interaction to Next Paint)
- Chrome DevTools Performance panel — record a user session and inspect long tasks (tasks taking over 50ms), which are the primary cause of poor INP. The Interactions track shows how long each interaction took from input to the next frame paint.
- Web Vitals Chrome Extension — displays live LCP, INP and CLS values as you interact with any page, making it easy to identify which specific interactions (button clicks, menu opens, form inputs) are driving poor scores.
- PageSpeed Insights — INP field data is available in the CrUX-powered section of the report for pages with sufficient traffic.
CLS (Cumulative Layout Shift)
- PageSpeed Insights — the lab-based CLS score highlights which elements are shifting and by how much. A score below 0.1 is good; above 0.25 is poor.
- Chrome DevTools Layout Shift Regions (Rendering panel) — enables a visual overlay highlighting which elements are causing shifts in real time as you load and interact with the page.
Mobile-First Experiences
Google uses mobile-first indexing, meaning it primarily uses the mobile version of your site for ranking purposes. Core Web Vitals scores are measured separately for mobile and desktop — and mobile scores are almost always lower. Prioritise mobile performance: test on real devices, reduce JavaScript payloads for mobile users, and ensure your layout is fully responsive.
Mastering Core Web Vitals is no longer optional — it's a strategic requirement for SEO success. If you need a helping hand with performance optimisation, get in touch.
