How can you effectively test image lazy loading for SEO?

What problems does lazy loading pose for Google crawling?

Lazy loading defers image loading until they enter or approach the viewport. This technique improves perceived performance but complicates life for Googlebot if implemented incorrectly.

Googlebot does not scroll automatically like a user. If your critical images depend on a scroll to load and you have not implemented the loading="lazy" attribute correctly, they may never be seen by the bot. The result: absence of indexing in Google Images and loss of context for page content.

What specific recommendations does Martin Splitt make?

Splitt suggests using the browser's DevTools to check loading behavior. The Network tab shows when each image loads and if it is visible to the engine. This is an effective manual approach for a few test pages.

For large-scale verification, he mentions Puppeteer (a headless browser automation tool) or other automated testing tools. He acknowledges that this approach is complex — implying that Google does not provide a turnkey tool for this diagnosis.

What are the implications for image indexing?

If Googlebot does not see your images during the crawl, they will not be indexed in Google Images. This is not just a performance issue — it’s a gap in your SEO visibility.

Images that provide semantic context (such as infographics, explanatory diagrams, product photos) must be immediately visible. Lazy loading should only apply to images below the fold and never to critical content above the fold.

• Googlebot does not scroll — lazy-loaded images without the native attribute risk being invisible
• The loading="lazy" attribute has been recognized by modern browsers and Googlebot since 2020
• Critical images must always load unconditionally (no lazy loading)
• Testing with DevTools Network + Lighthouse is a minimum — automation with Puppeteer remains complex
• The absence of indexing in Google Images can impact overall traffic, especially for e-commerce

Does this recommendation align with real-world observations?

Yes, and it is indeed a recurring issue observed on sites that have implemented custom JavaScript lazy loading without considering crawl constraints. Technical audits regularly show product images or key visuals missing from Google Images indexing even though they are perfectly visible to a user.

The nuance that Splitt does not address directly: Googlebot executes JavaScript, certainly, but with a limited rendering budget and sometimes delays that prevent capturing all deferred images. Scripts waiting for a scroll event or an IntersectionObserver do not always trigger as expected. [To verify]: Google has never published clear data on the success rate of JavaScript rendering for lazy-loaded images with third-party libraries.

Why does Splitt mention the complexity of Puppeteer?

Because he knows very well that few SEO teams have the technical resources to script large-scale tests with Puppeteer. It’s an implicit admission: Google does not provide an official tool to diagnose this problem at the site level.

Lighthouse and PageSpeed Insights give indications of non-lazy-loaded images (which slow down the initial load), but the opposite — detecting critical images poorly lazy-loaded — is not covered. You have to hack together your own solution or manually review key pages. For a site with 10,000 products, it’s unmanageable without automation.

What critical mistakes must be avoided at all costs?

The most common: applying lazy loading indiscriminately to all images, including those in the header, logo, main banner, and the first product image. These elements must load immediately, unconditionally.

Another pitfall: using a lazy loading JavaScript library that replaces the src attribute with data-src and does not provide fallbacks for bots. Googlebot can interpret JavaScript, but if the script fails or takes too long, the image remains invisible. The native loading="lazy" attribute is understood by Googlebot and is the most reliable method — but it is not backward compatible with all older browsers, hence the need for hybrid strategies.

How can you check that your images are visible to Googlebot?

First step: open DevTools (F12), go to the Network tab, filter for "Img", then reload the page. See which images load immediately and which only appear after a scroll. Images above the fold should all load without interaction.

Next, test the page with the URL Inspection tool from the Search Console. Click on "Test live URL", then "View tested page" to see the rendering as captured by Googlebot. If critical images are missing, you have a poorly configured lazy loading issue. This is the quickest and most reliable test for a spot diagnosis.

What tools can be used for large-scale verification?

To automate, Screaming Frog can render JavaScript and compare images detected with and without rendering. But it does not perfectly simulate Googlebot. Tools like OnCrawl or Botify can cross-reference server logs with crawl data to spot images never requested by Googlebot.

If you have the technical skills, Puppeteer or Playwright allow you to script a journey across hundreds of pages, take screenshots, and list loaded resources. It’s powerful, but it requires development and maintenance. For many teams, this is out of reach without support.

What should you do if you detect critical images that are poorly lazy-loaded?

Immediately exclude above the fold images from lazy loading. If you are using a JavaScript library, set up exclusion CSS classes or specific selectors. If you are using the native loading="lazy" attribute, remove it from priority images and add fetchpriority="high" on the main image.

Reinitiate a Google crawl via the Search Console after correction, then monitor indexing in Google Images. The delay can be a few days to several weeks depending on your site’s crawl frequency. Keep an eye on the Core Web Vitals: removing lazy loading from certain images can impact LCP if you do not compensate with other optimizations (compression, CDN, responsive images).

• Manually check key pages with DevTools Network and the URL Inspection tool
• Exclude all above the fold images from lazy loading
• Use the native loading="lazy" attribute for images below the fold
• Test Googlebot rendering with Search Console after each modification
• Monitor image indexing in Google Images via Search Console
• Establish regular monitoring (at least monthly) to detect regressions after site updates