Performance Tools

Image Optimization Checker

Check a page's images for missing dimensions, missing lazy loading, and oversized file sizes.

Enter a URL to check its images for missing width/height attributes, missing lazy loading, and oversized file sizes.

Checks up to 8 images found on the page.

More Performance Tools

Render-Blocking Resources Checker GZIP Compression Checker Performance Health Score Brotli Compression Checker CDN Detection HTTP Version Checker Page Size Checker Cache Headers Checker

JustChecker tracks your website's performance continuously, catching regressions before your visitors notice.

What Is the Image Optimization Checker?

It checks a page's images for common performance problems: missing width and height attributes (which cause layout shift), missing loading="lazy", and files over 300 KB.

When to Use It

When pages are heavy or jump around while loading.
When PageSpeed Insights flags image issues.

How to Use It

Enter the URL.
Review the flagged images.

Understanding the Result

Always set width and height (or CSS aspect-ratio) to reserve space. Lazy-load images below the fold, but not the main image at the top, which should load immediately. Convert large photos to WebP or AVIF.

Limitations

File sizes are checked for the first 8 images, and CSS background images are not included. Convert images with the WebP Converter.

Frequently Asked Questions

Without them, the browser doesn't know how much space to reserve for an image before it loads, causing the page layout to visually shift once it does - a poor user experience and a negative Core Web Vitals signal (Cumulative Layout Shift).

It tells the browser to defer loading an image until it's about to scroll into view, saving bandwidth and speeding up initial page load for images further down the page.

Up to 8 images per scan (a bounded, lightweight check), flagging any over 300 KB as a candidate for compression or a more efficient format like WebP or AVIF.