Core web vitals

What are core web vitals?

Core Web Vitals are Google's specific metrics that measure the quality of user experience on websites. They focus on the aspects of web performance that matter most to real users as they interact with pages. Introduced in 2020, these metrics have become a critical part of Google's page experience signals, which influence how websites rank in search results. Core Web Vitals measure loading performance, interactivity, and visual stability—three dimensions that directly impact how users perceive your site's quality and usability.

Why are core web vitals important for SEO?

Core Web Vitals are directly tied to your website's search ranking potential. Google uses these metrics as ranking factors, meaning sites with strong Core Web Vitals scores have a competitive advantage in search results. Poor performance can limit your visibility, while excellent scores can boost your rankings. Beyond SEO benefits, these metrics correlate strongly with user satisfaction—faster, more stable sites typically see lower bounce rates, higher engagement, and better conversion rates. When users have a smooth experience on your site, they're more likely to stay, explore, and take desired actions.

What are the three main core web vitals metrics?

Largest Contentful Paint (LCP) measures loading performance by timing how quickly the largest content element becomes visible. This could be an image, video, or text block. For good user experience, LCP should occur within 2.5 seconds of page load.

First Input Delay (FID), being replaced by Interaction to Next Paint (INP), measures interactivity. FID tracks the time from when a user first interacts with your page to when the browser can respond. INP measures the responsiveness of all interactions. A good FID score is under 100 milliseconds, while INP should be under 200 milliseconds.

Cumulative Layout Shift (CLS) measures visual stability by quantifying how much page elements unexpectedly move during loading. This prevents frustrating experiences where users try to click something that suddenly shifts. A good CLS score is 0.1 or less.

How can you measure core web vitals?

Several tools make measuring Core Web Vitals straightforward. Google PageSpeed Insights provides both lab and field data for your pages, showing performance across real users and simulated environments. Google Search Console includes a dedicated Core Web Vitals report that identifies groups of pages with similar issues. Chrome's Lighthouse tool offers detailed audits with specific recommendations for improvements. For ongoing monitoring, Chrome User Experience Report (CrUX) data shows how real users experience your site over time. The Web Vitals JavaScript library allows developers to measure these metrics programmatically within their own analytics.

How do you improve core web vitals scores?

To improve LCP, optimize your critical rendering path by reducing server response times, minimizing CSS and JavaScript, and properly sizing and compressing images. Consider implementing content delivery networks and browser caching for faster delivery.

For better FID/INP scores, minimize or defer JavaScript execution, break up long tasks into smaller chunks, and optimize event handlers. Remove unnecessary third-party scripts that block the main thread during critical user interactions.

To reduce CLS, always specify dimensions for images and videos in your HTML, reserve space for ads and embeds, and avoid inserting content above existing content unless responding to user interaction. Use transform animations instead of those that trigger layout changes.

Implementing these improvements often requires balancing competing priorities, but even incremental changes can significantly enhance both user experience and search visibility.