Signal, CLS, and Google Lighthouse

Put simply, Signal has no effect on cumulative layout shift scores.

This is because CLS is primarily affected by a publisher's website setup. These scores are calculated by a few different factors, and we've included them below.

A poor CLS score will occur when one or a combination of the following is occurring on the page:

• images are being loaded to the page without the proper dimensions

• ads are loaded to the page without proper dimensions

• content is dynamically injected into the page 

• web fonts create a flash of invisible text (FOIT) or a flash of unstyled text (FOUT)

• Actions occur on the page that is waiting for a network response before updating the domain object model (DOM)

Signal utilizes the existing on-page setup put in place by the publisher, and executes operations also configured by the publisher. 

Every Signal script is precompiled, then compiled again, then compressed. Once the compiling/compressing is completed, Amazon Cloudfront is used to deliver the code to the page. Once on the page, Signal utilizes asynchronous loading to ensure the full page is parsed & loaded before the script is executed on the page. 

Lastly, the data collected from Signal is executed when we detect that the user is not engaged, meaning that any user session is not interrupted or slowed down.

Google Lighthouse & Signal

Google Lighthouse is an open-source tool for web developers to better understand their site's quality scores. It gives developers an understanding of the quality of page experiences with metrics from Google. 

Those metrics are:

• Is the website mobile-friendly?

• Are images set up for desktop & mobile devices?

• Is the site safe for users?

  • does the site contain malware?

  • does the site have a good user experience?

• Is the site in HTTPS?

• Are there any intrusive ads? 

  • is there a good CLS score?

• What are the site?s core web vitals?

  • how does the site load?

  • how interactive is the site?

  • what is the visual stability of the site?

As previously mentioned, Signal utilizes the publisher's setup on the page, as well as the ad inventory that is also set up by the publisher. 

Poor scores from Google Lighthouse are indicative of a poor user experience that needs to be fixed on the publisher's website. It could also stem from a publisher's ad supply containing excessively heavy ads.