Google is currently testing the Visual Stability Index (VSI), a new Core Web Vital metric that could replace — or complement — CLS (Cumulative Layout Shift) starting in 2027. Unlike CLS, which measures layout shifts during initial page load, VSI monitors visual stability throughout the entire user session, including after interactions.
This evolution reflects a reality: modern sites continue to shift after loading (modals, notifications, delayed ads). VSI captures this instability that current CLS misses.
1. VSI measures stability across the entire session, not just at load
CLS stops measuring after the first 5 seconds (or after the first user click). VSI continues measuring shifts for the entire visit duration. This means a cookie banner appearing 10 seconds after load, or a lazy-loaded ad, will now count toward the stability score.
2. User interactions are factored in
VSI measures shifts caused by user actions: opening a dropdown that pushes content below, clicking an accordion that shifts the rest of the page down, or seeing content “jump” when hovering over an interactive element. These micro-shifts disrupt experience without being captured by traditional CLS.
3. Ads and modals are in the crosshairs
Promotional pop-ins, auto-opening chatbots, and delayed consent banners are the main VSI targets. Google wants to penalize sites that maintain clean CLS at load but then bombard users with shifting content.
To prepare: always reserve space for delayed elements (fix ad slot heights, don’t inject content above existing content without pushing the rest of the page down).
4. How to prepare your site for VSI
Even though VSI isn’t an official ranking factor yet, you can start optimizing for it:
- Measure post-load shifts: use Chrome DevTools (Performance Monitor) and enable “Layout Shift Regions” to visualize all page movements during a browsing session.
- Fix dynamic container heights: if an element loads via AJAX (customer reviews, recommended content), give it a minimum height from the start.
- Avoid aggressive pop-ins: if you must show a modal, slide it from bottom or right rather than abruptly overlaying it in the center (which shifts visual perception without shifting DOM — but VSI might measure that too).
- Test your ads: programmatic banners are notoriously unstable. Switch to fixed-height slots or use “sticky” formats that don’t push content.
5. VSI probably won’t replace CLS, it will complement it
Google rarely tests a metric to abandon another. Most likely scenario: VSI becomes a fourth Core Web Vital alongside LCP, INP, and CLS. This means sites will need to optimize both initial load (CLS) AND in-session stability (VSI).
Real impact: sites that abuse delayed ads or pop-ins risk losing rankings even with perfect CLS. “Clean” sites without post-load disruptions will have a competitive advantage.
Frequently Asked Questions About Visual Stability Index
Is VSI already a Google ranking factor?
Not yet. Google is currently testing it in Chrome Canary and gathering field data. Official integration into Core Web Vitals is expected no earlier than 2027, based on Google’s signals.
How do I measure my current VSI?
There’s no official public tool for VSI yet. You can install Chrome Canary and enable experimental performance flags, but the metric isn’t stabilized yet. Meanwhile, focus on optimizing CLS and eliminating post-load shifts (chatbots, delayed banners).
Does good CLS guarantee good VSI?
Not necessarily. CLS measures the first 5 seconds, VSI measures the entire session. A site can have CLS of 0.05 (excellent) and mediocre VSI if pop-ins appear later. Conversely, a site with no delayed disruption will have good VSI even with average CLS.
Do CSS animations count in VSI?
Smooth animations (CSS transitions, transforms) generally don’t cause layout shifts and shouldn’t affect VSI. However, an animation that modifies an element’s height (expand/collapse) can shift content below — that’s where VSI will measure it.
What if my site has lots of dynamic content?
Favor progressive loading with fixed-height placeholders (skeleton screens), rather than injecting variable-height content. For interactive elements, use smooth transitions (CSS transform/opacity) rather than abrupt layout changes.
Conclusion: anticipate rather than react
VSI marks a logical evolution of Core Web Vitals: measuring real, complete user experience, not just initial load. Sites that anticipate this metric by eliminating post-load disruptions now will have a competitive edge when VSI becomes an official ranking factor.
Test your site with a complete SEO audit to identify visual stability and Core Web Vitals issues right now.
