Core Web Vitals: LCP, INP, CLS and How to Improve Them

Core Web Vitals are a set of metrics defined by Google to measure the quality of user experience on a page. They are part of the page experience signals Google takes into account, although excellent, relevant content can still rank well with average scores.

The three metrics

• LCP (Largest Contentful Paint): the time it takes to display the largest visible element (often an image or a block of text). Good: 2.5 seconds or less.
• INP (Interaction to Next Paint): how responsive the page is when the user clicks, taps or types. Good: 200 milliseconds or less.
• CLS (Cumulative Layout Shift): visual stability, meaning unexpected layout shifts. Good: 0.1 or less.

INP replaced the former FID metric in March 2024. To be rated "good", a page must meet these thresholds for at least 75% of visits, measured in the field.

Where to measure

• Google Search Console: the "Core Web Vitals" report groups your URLs by status (good, needs improvement, poor).
• PageSpeed Insights: real-user data (when available) and a detailed diagnosis.
• Lighthouse in Chrome: lab testing, useful during development.

Improving LCP

• Compress images and use modern formats (WebP, AVIF).
• Don't lazy-load the main image that is visible as soon as the page opens.
• Reduce server response time and use caching or a CDN.
• Limit render-blocking resources (non-essential CSS and JavaScript).

Improving INP

• Reduce and split heavy JavaScript.
• Remove or defer unnecessary third-party scripts (widgets, trackers).
• Avoid long tasks that block the browser.

Improving CLS

• Always set the width and height of images and videos.
• Reserve space for ads and banners.
• Avoid inserting content above content that is already displayed.

Start with the pages that bring the most traffic or revenue: that is where each improvement pays off the most.