Lazy Load Checker
Check if your website uses lazy loading for images. Get optimization recommendations.
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Best Practices
Use loading="lazy"
Add the native lazy loading attribute to images below the fold. This is supported by all modern browsers.
Avoid lazy loading above-the-fold
Images visible on initial page load should not be lazy loaded, as this delays LCP.
Add width and height
Always specify image dimensions to prevent layout shifts (CLS) when images load.
Use decoding="async"
For non-critical images, add decoding="async" to prevent blocking the main thread.
Consider IntersectionObserver
For more control over lazy loading, use IntersectionObserver for custom implementations.
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About This Tool
Check whether a web page's images use lazy loading — the technique that defers off-screen images so the page renders fast. Enter a URL and get a per-image report: which images load immediately, which defer, which lack dimensions (causing layout shift), and what the total image weight is. Page owners use it to find the images slowing down their site; it complements Lighthouse with a plain, image-focused view.
How to Use This Tool
- Enter the page URL and start the check — the page loads in a sandboxed frame.
- Read the summary: total images, eagerly loaded, lazily loaded, missing width/height attributes.
- Sort the table by size to spot the heaviest above-the-fold offenders.
- Flag images that load eagerly despite being below the fold — those are your quick wins.
- Apply loading="lazy" plus explicit width/height to flagged images in your code, then re-run to confirm.
Advantages & Use Cases
Diagnose a slow WooCommerce category page where 30 product photos load at once, verify a new theme respects lazy loading, or audit a blog before a page-speed push. Agencies run it during handover to prove image optimization was applied.
Supported Formats & Recommendations
- Works with any public URL; JavaScript-rendered pages are supported since the check runs a real browser engine.
- Reports image formats too — a page serving JPG where WebP would do shows up instantly in the weight column.
- Best combined with our Image Compressor: check, compress the offenders, re-upload, re-check.
How We Test This Tool
We verify the checker against reference pages: a page with 10 lazy images must report 10 lazy, a no-dimensions test page must flag layout-shift risks, and results must stay stable across three consecutive runs of the same URL (no flaky counting).
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Helpful Resources
Frequently Asked Questions
What's a good lazy-loading score?
Everything below the fold lazy, everything above the fold eager. First 1-2 hero images should load immediately (they affect LCP); the rest should defer.
Why do my images need width and height attributes?
Without them the browser can't reserve space, so content jumps when images arrive — that's Cumulative Layout Shift, a ranking-affected metric. The checker flags each offender.
Does lazy loading hurt SEO?
Not when implemented with standard loading="lazy" — crawlers render the full page. Problems only arise with JavaScript tricks that hide images from the crawler; the checker spots those patterns.