Cumulative Layout Shift
Here's how I actually work with cumulative layout shift when the stakes are real.
Start here
- CLS is one of Google’s Core Web Vitals and is designed to measure visual stability.
- It measures unexpected layout shifts, not shifts caused by user actions such as clicking a button.
- Google describes CLS as the largest burst of layout shift scores across the full lifecycle of a page.
CLS affects perceived page stability and user experience, so it is a practical SEO and UX quality signal. For SEO practitioners, low CLS helps reduce frustrating jumps that can hurt engagement and page quality, especially on mobile.
Example
CLS is one of Google’s Core Web Vitals and is designed to measure visual stability.
Quick start
- Define the goal for this topic.
- Check the live SERP format.
- Improve one page that matches the intent.
- Measure in Google Search Console.
Common mistakes
- Treating the topic as a one-time task
- Ignoring search intent
- Copying tactics without checking your SERP
Next step
Quick answers
What is a good CLS score?
A good CLS score is less than 0.1. Scores between 0.1 and 0.25 need improvement, and scores above 0.25 are poor.
How can I improve cumulative layout shift?
Set explicit dimensions on images and videos, reserve space for ads and embeds, use font-display: swap for web fonts, and avoid inserting dynamic content above existing content after the page has loaded.
Does CLS affect SEO?
Yes, CLS is one of Google's Core Web Vitals and is a ranking factor in the page experience signal. Poor CLS can negatively impact search rankings, especially for mobile.
Sources
Primary documentation is linked directly. Anything commercial is marked nofollow.
- web.dev: Cumulative Layout Shift (CLS) — Primary Google explanation of the metric and how CLS is defined.
- web.dev: Optimize Cumulative Layout Shift — Google guidance on how to reduce CLS and target thresholds.
- MDN Glossary: CLS — Clear glossary definition of CLS and what counts as unexpected shift.
Notes from Callum Bennett.