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