The greatest burst of layout shift scores for each not-expected layout shift that happens over the course of a page is measured by Cumulative Layout Shift(CLS). Any time a visible element moves from one rendered frame to the next, it’s called a layout shift.
A burst of layout shifts, sometimes referred to as a session window, is when one or more layout shifts happen quickly one after the other, with a maximum window duration of five seconds and less than one-second elapsing between shifts.
The session window containing the highest total score of all layout shifts made during that window has the biggest burst.
What is a good CLS score?
A large number of unexpected layout changes on a web page are indicated by a high CLS score. At the same time, a page that is entirely static may receive a score of zero.
To assist website owners in assessing and raising their CLS scores, Google has established a baseline for all Core Web Vitals metrics:
- Good: Google’s criteria states that a score of less than 0.1 is acceptable.
- Needs improvement: a value between 0.1 and 0.25 suggests that adjustments are needed to minimize unexpected shifts.
- Poor: a score of more than 0.25 can negatively impact your website’s ranking.
Different web pages and screens on a website may have different CLS scores. Changes in mobile screen layouts have a more noticeable effect on mobile user experiences.
What Issue Is Leading to a Low CLS Score?
Consider the following factors if a website gets a low CLS score:
- Images, videos, embeds, iFrames, and banner advertisements without regard to size requirements.
- Dynamic content that is above the viewport and does not have a screen size placeholder.
- Personalized fonts that alter the rendering process.
These activities frequently result in larger unexpected layout shifts since they wait for a network response before uploading items.
How to boost your Cumulative Layout Shift Score?
As a ranking factor, CLS score optimization will increase visitors to your website. These are four strategies to raise your CLS score, along with an explanation of their effects and degrees of difficulty.
- Specifying Image and Video Dimensions
- Configuring iFrames, embeds, and banner ads width and height
- When using custom fonts, use font:display
- Examining Content Injected Dynamically
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