LCP & CLS Culprit Finder

It runs a real Google Lighthouse (PageSpeed) test and pulls out the element-level details most tools hide: the exact DOM element that is your Largest Contentful Paint (LCP), the specific elements causing Cumulative Layout Shift (CLS), images served without width/height, and the render-blocking CSS/JS — each with a concrete fix. It turns an abstract score into a precise to-do list.

Your LCP is decided by one element — usually the hero image, a heading, or a large block of text. If you don’t know which element it is, you can’t fix it. Once you know, the fixes are clear: preload it, serve it in a modern format, size it correctly, and never load it lazily or via JavaScript.

When an image has no width and height, the browser doesn’t know how much space to reserve, so content jumps when the image finally loads — that jump is layout shift (CLS). Adding explicit width and height attributes (or a CSS aspect-ratio) lets the browser reserve the space up front and keeps the page stable.

This is a lab test — a single controlled Lighthouse run on a simulated mobile device, which is what surfaces the exact culprit elements. For how real visitors actually experience your Core Web Vitals over time, use the CrUX History Trends tool, which uses Google’s real-user field data.