Free Performance Tool
CLS Tester
Cumulative Layout Shift measures how much your content jumps around while it loads — the reason people tap the wrong button and leave. Enter any public URL and we'll show you exactly which elements shift, why they shift, and how to fix each one.
A late-loading image pushes the text down after the page has already rendered. Google scores that jump — and so does everyone who was mid-sentence when it happened.
Questions about layout shift
- What is a good CLS score?
- Google considers 0.1 or below good, up to 0.25 needs improvement, and anything above 0.25 poor. The score is measured at the 75th percentile of real page views.
- Why does my lab score say zero when my page clearly jumps?
- The lab test loads your page but never scrolls or interacts with it. Shifts caused by lazy-loaded images entering the viewport, cookie banners, sticky headers, or ad slots only happen once a real person starts using the page, so they do not appear in a lab run.
- Where does the real-user data come from?
- The Chrome User Experience Report, which aggregates anonymised measurements from real Chrome users over a rolling 28-day window. A page needs enough traffic to appear, so smaller sites often only have data at the whole-site level.
- Does layout shift actually affect my Google rankings?
- CLS is one of Google's Core Web Vitals, which are a ranking signal. The larger cost is usually commercial rather than algorithmic: content that moves while people read makes them tap the wrong thing and leave.
- How do I fix layout shift?
- Reserve space before content loads. Set width and height on images and video, give ad and embed slots a fixed container height, avoid inserting content above existing content, and use font-display: optional so web fonts do not reflow text.