Core Web Vitals
Google's metrics for measuring page speed, responsiveness, and visual stability.
The Definition
Core Web Vitals are a set of user experience metrics defined by Google: Largest Contentful Paint (LCP) measures loading speed, Interaction to Next Paint (INP) measures responsiveness, and Cumulative Layout Shift (CLS) measures visual stability. They are a confirmed Google ranking factor.
Why It Matters
Sites that meet Core Web Vitals thresholds (LCP < 2.5s, INP < 200ms, CLS < 0.1) rank better and provide better user experiences. Poor scores lead to higher bounce rates and lost revenue — a 1-second delay in page load can reduce conversions by 7%.
Best Practices
Measure Core Web Vitals using real user data (CrUX) rather than relying solely on lab tools like Lighthouse
Focus on LCP first — it has the highest correlation with search ranking improvements among the three metrics
Preload the LCP element (hero image or above-the-fold content) to start loading it as early as possible
Eliminate layout shifts by always specifying width and height attributes on images and video elements
Reduce JavaScript execution time to improve INP — break up long tasks and defer non-critical scripts
Monitor CWV scores continuously using Google Search Console Core Web Vitals report
Mistakes to Avoid
- 1
Optimizing only for Lighthouse scores instead of real field data — lab and field metrics often differ significantly
- 2
Ignoring INP (Interaction to Next Paint) which replaced FID in 2024 as the responsiveness metric
- 3
Loading web fonts without font-display: swap, causing invisible text flashes that hurt both LCP and CLS
- 4
Adding third-party scripts (analytics, ads, chat widgets) without measuring their impact on Core Web Vitals
Audit Checks
How Digispot AI identifies and fixes related issues
This page was rendered in a real browser but no Core Web Vitals (LCP, CLS, FCP, TTFB) were measured — the performance reading is missing for this page.
Impact: Without Core Web Vitals we cannot grade this page's real-world loading performance, so the Performance score is shown as not-measured rather than a real number. It usually means the capture timed out or the page never settled, not that the page is slow.
Re-run the crawl for this page — capture failures are often transient (timeout, a never-idle page, or a heavy render). • If it recurs on the same page, check for long-running scripts or infinite animations that stop the page from settling. • Verify the page renders within the crawler's render/idle timeout for very large pages.
Some images aren't optimized for the web — they're larger than they need to be.
Impact: Heavy images slow rendering and hurt Core Web Vitals, especially on mobile.
Compress images and use modern formats (WebP/AVIF). • Resize images to the size they actually display. • Lazy-load images below the first screen.
The page is slow to respond when a visitor interacts with it — taps, clicks and key presses lag (Interaction to Next Paint, or INP, over 200ms).
Impact: INP is a Core Web Vital and Google ranking signal; a laggy interaction makes the page feel broken and drives visitors away.
Break up long JavaScript tasks so the main thread can respond sooner. • Defer or remove scripts that aren't needed for the first interaction. • Move heavy computation off the main thread (web workers).
Content jumps around as the page loads — buttons or text shift under the reader (a high Cumulative Layout Shift, or CLS, over 0.1).
Impact: Layout jumps frustrate visitors with mis-clicks and lower your Google ranking.
Set explicit width and height on every image and video. • Reserve space for ads, embeds, and banners before they load. • Avoid inserting content above what the reader is already viewing.
The HTML document alone is larger than 2MB — past Google's documented 2MB indexing limit. Images, CSS and JS are fetched separately and do NOT count toward this.
Impact: Google only indexes the first 2MB of HTML, so any content past that point in the document risks never being indexed.
Trim large inline scripts and JSON embedded in the HTML. • Paginate huge lists and move bulk data out of the initial HTML. • Enable server-side compression to shrink the document below 2MB.
The biggest thing on the page — usually the hero image or main heading — takes more than 2.5 seconds to appear (its Largest Contentful Paint, or LCP).
Impact: Google uses LCP as a ranking signal, and visitors often leave before a slow page finishes loading.
Compress the largest above-the-fold image and serve it as WebP or AVIF. • Preload that hero image and your main web font so they load first. • Remove or defer render-blocking scripts and CSS.
Related Terms
Largest Contentful Paint (LCP)
A Core Web Vitals metric measuring when the largest visible element finishes rendering.
Cumulative Layout Shift (CLS)
A Core Web Vitals metric measuring how much page content unexpectedly shifts during loading.
Page Speed
How quickly a web page loads and becomes interactive for users.