Image CLS Checker

Image CLS Checker lists each image on a page with its declared width and height, marks the ones that have neither, and flags the first image if it is lazy-loaded.

Two faults are judged per image. Missing width or height is a fail, because the browser reserves no space for that image and everything below it jumps when it finally loads. The first image carrying loading="lazy" is a warning, since the image most likely to be the largest contentful element is the last one that should be deferred. The coverage figure and risk band are derived from the count of unsized images rather than being a measured CLS value, because a real CLS number only exists while a page renders — and since the markup is the only evidence, an image sized purely in CSS reads here as unsized.

With a URL, ShortTrick's server fetches the HTML and reads the img attributes out of it; no image file is ever requested, so no image host records a visit. The fetch is made with our own user agent, carries nothing of yours, and the markup is not kept. Pasting HTML keeps the whole check local to your tab.

Finding the images on a page that make content jump, checking a hero image is not lazy-loaded, confirming a template adds dimensions to the img tags it generates, and auditing images before chasing a CLS failure in Search Console.

Also known as: prevent cumulative layout shift · image width height audit · check image cls · test image cls