CLS CheckerPreliminary technical test
Find technical candidates for layout shifts, especially images, iFrames, and dynamic media with no reserved space.
Technical pre-testing without browser rendering. Own scores of 0–100 mean: higher = less recognized risk signals. No measured LCP, INP or CLS values. TTFB is measured on the server side.
Ideal for editorial pages, shops, ad spaces, embeddeds and visual landing pages.
Results
Technical pre-checking of a URL. For a crawl over many URLs, use the premium audit.
Findings
Detailed hit
Practical example · for illustration
Reserve space for pictures even before downloading
Example: An image without width and height moves text down after loading. Specify the intrinsic dimensions and use appropriate CSS rules such as max-width:100% and height:auto for responsive display. For variable embeds, aspect-ratio can reserve space.
What does not prove the result
Missing HTML measures are a candidate, not a measured layout shift: CSS can already reserve space. Also check the Layout Shift events in the browser for interactions.
Deepen with PageSpeed Insights and available field data · Google's Definition of Core Web Vitals
What the CLS Checker evaluated
The pre-check evaluates the retrieved HTML and a limited sample of linked resources. It does not execute JavaScript and does not simulate user interactions. Findings are concrete occasions for an examination in the browser; an inconspicuous result does not exclude performance problems.
From a single check to Core Web Vitals Audit
The audit examines multiple URLs and helps to find recurring technical patterns in templates. This way you can see if a change affects several pages and where you can start the implementation.
Questions about CLS Checker
What causes CLS?
Frequently, fixed image dimensions, reserved display areas, stable embedded sizes or font fallbacks are missing.
Can CLS also be created by JavaScript?
Yes. Dynamically inserted banners, consent elements or widgets can move layouts.
Why are there standalone tools in addition to the audit?
Individual tools help with a specific URL or technical problem. The audit compares these signals across multiple URLs and shows recurring patterns.
Is the individual check free of charge?
Yes. The standalone tools check a single URL. For larger crawls, complete tables and CSV export, the premium audit is planned.