Core Web Vitals Checker

Core Web Vitals Checker reads a page and rates its LCP, CLS and INP exposure as low, medium or high, naming the specific thing in the markup responsible for each rating.

There are deliberately no metric values here, only risk bands with their causes attached, because none of the three metrics can be obtained without rendering the page. The LCP band comes from the server response time and the count of blocking scripts and stylesheets; the CLS band from how many images declare no width and height, pushed to high by an @import inside a stylesheet; the INP band from the DOM node count and from inline scripts over 50KB sitting on the main thread. Each band lists the reasons it reached that level, which is what makes it actionable where a score would not be.

The page is fetched by ShortTrick's server through its inspect route rather than by your browser, so the site you check logs our request and not yours. Only the HTML is read — no stylesheet, script or image is downloaded — and nothing is stored. Pasting markup avoids the request, although the response time that drives the LCP band is then unavailable and a default value stands in for it.

Finding which parts of a template put LCP at risk before measuring in a browser, listing the images responsible for layout shift, judging whether a heavy inline script is a plausible INP problem, and triaging a page Search Console has flagged.

Also known as: lcp checker · inp tester · cls calculator · check core web vitals · core web vitals test · test core web vitals