CLS Checker - Journey Further is a free Chrome add-on developed by Journey Further. This tool is designed to test and debug cumulative layout shifts (CLS) in the browser. It utilizes data from the Chrome Performance API to measure and display the layout shifts that occur when a page is loaded.

With CLS Checker, users can easily identify and track layout shifts on webpages. The tool provides a list of layout shift scores and visualizes the shifts on the webpage using green squares to indicate the starting position of elements and red squares to indicate where the elements were shifted to.

Overall, CLS Checker - Journey Further is a useful tool for web developers and designers who want to optimize the layout stability of their webpages. It provides valuable insights and visualizations to help identify and fix layout shifts, resulting in a better user experience.