Checks
Image dimensions
Checks that images declare width and height attributes so browsers can reserve layout space before the file finishes loading, preventing content from jumping around.
What this check looks for
This check inspects every content image and flags any missing either a width or height attribute (or both). If any images are missing dimensions, it warns, listing each one. A page with no images reports "na"; a page where every image declares both dimensions passes.
Why it matters
When a browser doesn't know an image's dimensions ahead of time, it can't reserve space for it in the layout, so the surrounding text and elements shift down the moment the image finishes loading — this is exactly what Cumulative Layout Shift measures, and it's one of the three Core Web Vitals search engines use as a ranking signal. Beyond the ranking impact, a page that visibly jumps around while loading reads as janky and unpolished, which erodes trust in the content itself regardless of how good that content is.
How to fix it
Declare explicit width and height on every image (CSS can still control the rendered size responsively):
<!-- No dimensions declared: browser can't reserve space -->
<img src="/hero.webp" alt="Acme wireless headphones"><!-- Fixed: intrinsic dimensions declared, CSS controls display size -->
<img src="/hero.webp" alt="Acme wireless headphones" width="1600" height="900" style="max-width: 100%; height: auto;">Use the image's actual intrinsic pixel dimensions in the attributes — the browser uses them only to compute aspect ratio for reserved space, not to force a fixed display size.
See how your site scores on this check