Is lazy loading really a must-have SEO performance lever you should activate systematically?

What is lazy loading and why is Google talking about it now?

Lazy loading (or deferred loading) consists of loading resources — images, videos, iframes — only when the user scrolls toward them. Instead of downloading all content when the page displays, the browser waits for the right moment.

This technique is not new, but its adoption exploded with the native loading="lazy" attribute in HTML5. Google mentions it here in a performance context: reducing initial weight improves Time to Interactive (TTI) and can positively impact Core Web Vitals.

How does lazy loading reduce initial page load?

A page with 50 images of 200 KB each weighs 10 MB. If the user never scrolls to the bottom of the page, why download these 10 MB? Lazy loading limits initial weight to visible content (the "above the fold").

Concretely, the browser loads only resources within the viewport. As soon as the user scrolls, the following images load with a slight delay. The impact on Largest Contentful Paint (LCP) can be significant — provided the LCP image itself isn't lazy-loaded, obviously.

What are the risks for SEO?

Google indexes pages by simulating user behavior, but Googlebot does not scroll systematically like a human would. If your critical images (logos, product visuals, infographics) are lazy-loaded, they may not be indexed — or with a delay.

The crawler loads the HTML, executes JavaScript, but doesn't always trigger scroll events. Result: some images remain invisible to Google Images. This is an arbitrage to manage between user performance and SEO visibility.

• Lazy loading = deferred loading of resources outside viewport
• Improves TTI and can boost LCP if properly implemented
• Risk: images not indexed if Googlebot doesn't scroll
• Never lazy-load the LCP image or critical above-the-fold visuals

Is this recommendation consistent with real-world observations?

Yes, but with a significant caveat. Google has been preaching lazy loading for years, especially since native integration in Chrome. Tests show that the loading="lazy" attribute does effectively improve performance metrics — when used below the initial viewport.

The problem is that many developers apply lazy loading everywhere, including on critical images. Result: disastrous LCP, images that only display after 2 seconds, and Core Web Vitals scores that plummet. Google says "manage heavy content," but doesn't specify where to draw the line.

What nuances should be added to this statement?

Gary Illyes remains deliberately vague about SEO impact. He talks about "reducing initial load," but says nothing about image indexation. Yet, this is the crucial point for an SEO professional.

If you have an e-commerce site with 20 product visuals per page, lazy-loading everything except the first 3 can improve perceived loading time. But if your images aren't indexed in Google Images, you lose a traffic channel. [To verify]: Google claims Googlebot handles lazy loading, but real-world feedback shows significant indexation delays.

In what cases can this technique be counterproductive?

Lazy loading becomes toxic in three situations. First, if you apply it above the fold: the LCP image loads deferred, the browser waits, LCP explodes. Second, on pages with little content: if you only have 3-4 images, performance gain is negligible and partial indexation risk increases.

Finally, on high-stakes SEO Images sites — fashion, decor, stock photography. If your business relies on Google Images, lazy-loading without selective preload strategy is like shooting yourself in the foot.

What should you do concretely to implement lazy loading without breaking anything?

First step: identify above-the-fold images. Use Chrome DevTools to simulate different viewports (mobile, tablet, desktop) and spot visuals visible immediately. These images must load in eager mode (default) or with a preload.

Next, apply loading="lazy" only to images below the fold. If your CMS (WordPress, Shopify) lazy-loads everything by default, force eager behavior on the first X images. Then test with Lighthouse and verify your LCP hasn't regressed.

What mistakes must you avoid at all costs?

Never lazy-load the hero banner image, primary product logo, or any visual critical to immediate user experience. Some WordPress themes apply lazy loading blindly — audit your source code.

Also avoid lazy-loading images in carousels or sliders above the fold. The user can click before the next image loads, creating a degraded experience. And most importantly, don't rely solely on Lighthouse scores: verify actual indexation in Google Search Console and Google Images.

How do you verify your implementation is optimal?

Test with PageSpeed Insights and check that the "Defer offscreen images" audit doesn't flag critical images. Use Search Console to track your image indexation: if indexed images drop after lazy loading activation, that's a red flag.

Also analyze server logs to verify Googlebot loads your images. If you see HTTP requests for HTML but not for images, lazy loading is blocking the crawler. Finally, compare actual performance (CrUX) to lab tests: the gap can reveal implementation issues.

• Identify above-the-fold images and exempt them from lazy loading
• Apply loading="lazy" only to resources outside the initial viewport
• Verify the LCP image loads in eager mode or with preload
• Audit image indexation in Google Search Console after deployment
• Test on multiple viewports (mobile/desktop) to avoid regressions
• Monitor Core Web Vitals in real conditions (CrUX)