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.
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.