Core Web Vitals are the three metrics Google uses to measure real-world page experience, and they're a confirmed ranking factor — but the bigger cost usually isn't your search position, it's the visitors who bounce before the page even finishes loading.
The three metrics, in plain terms
LCP (Largest Contentful Paint) — how long until the biggest visible element (usually a hero image or heading) finishes rendering. Good: under 2.5 seconds. This is your "does the page feel like it loaded" number.
INP (Interaction to Next Paint) — how long the page takes to visibly respond after a click, tap, or keypress. Good: under 200 milliseconds. This is your "does the page feel stuck" number — a slow INP is why a button click seems to do nothing for a beat.
CLS (Cumulative Layout Shift) — how much visible content jumps around as the page loads (an image popping in and pushing text down, a late-loading ad shoving the button you were about to click). Good: under 0.1. This is your "did I just click the wrong thing" number.
Why Google — and your visitors — care
Google added Core Web Vitals as a ranking signal because they correlate strongly with whether someone actually has a good experience on a page, not just whether the content is relevant. In practice, a slow or janky page loses visitors regardless of ranking — bounce rate climbs sharply once LCP passes about 3 seconds, well before most people would call the site "broken."
The most common causes of failing scores
- LCP: unoptimized images (wrong format, no compression, no responsive sizing), render-blocking JavaScript or CSS, slow server response time.
- INP: heavy JavaScript execution on the main thread — often from a bloated framework bundle, too many third-party scripts (analytics, chat widgets, ad tags all fighting for the same thread), or a site that hydrates far more interactivity than the page actually needs.
- CLS: images and embeds without explicit width/height (so the browser can't reserve space before they load), web fonts that swap in and reflow text, content injected above existing content (a cookie banner or promo bar that shifts everything down after load).
Where this connects to redesign vs. rebuild
A site that's failing Core Web Vitals badly is usually a sign the underlying build needs work, not just the visuals — see our note on redesign vs. rebuild. A heavy page builder, an unoptimized image pipeline, or a JavaScript-framework choice that doesn't fit the content are architecture decisions, and they're expensive to patch around without addressing the root cause.
Every site we build is checked against Core Web Vitals as part of QA before launch, not as an afterthought — see what's included on our websites page.