Ever wondered why your website’s loading performance isn’t improving despite implementing lazy loading everywhere? Google’s Martin Splitt and John Mueller recently shed light on a critical mistake many developers make – and it’s costing sites their Largest Contentful Paint scores.
During a recent Search Off the Record podcast episode, the Google team revealed how blanket lazy loading can actually harm your Core Web Vitals. The discussion centered around a real issue they discovered on developers.google.com, where their content management system defaulted every image to lazy loading.
“The content management system that we are using for developers.google.com defaults all images to lazy loading, which is not great,” Splitt explained during the podcast.
The Lazy Loading Performance Trap
Here’s what happens when you lazy load your hero images and above-the-fold content:
Normal Image Loading Process:
- Browser’s preload scanner identifies critical images immediately
- High-priority fetching begins early in the loading process
- Hero image paints quickly, optimizing LCP timing
Lazy Loading Gone Wrong:
- Critical images get deprioritized by the browser
- Loading waits until layout calculations complete
- Hero images compete with other resources for bandwidth
- LCP timing gets pushed significantly later
Splitt was clear about the consequences: “If you are using lazy loading on an image that is immediately visible, that is most likely going to have an impact on your largest contentful paint. It’s like almost guaranteed.”
Why Your LCP Suffers With Improper Lazy Loading
Largest Contentful Paint measures when your viewport’s largest text block or image fully renders. When you apply loading="lazy" to above-the-fold elements, you’re essentially telling the browser to treat your most important visual content as low priority.
This creates a cascade of performance issues:
- Resource Competition: Scripts, stylesheets, and other assets load first
- Delayed Rendering: The largest contentful element waits in queue
- Network Bottlenecks: Slower connections amplify the delay
- Layout Shifts: Missing width/height attributes compound the problem
The impact becomes more pronounced on mobile devices and slower networks, where every millisecond counts toward user experience.
SEO Implications of Lazy Loading Libraries
Modern browsers support native lazy loading through the loading attribute, eliminating the need for bulky JavaScript solutions. However, many sites still rely on older libraries that can create SEO problems.
“Browsers got a native attribute for images and iframes, the loading attribute, which makes the browser take care of the lazy loading for you,” Splitt noted.
Legacy lazy loading implementations often store image URLs in custom data attributes instead of standard src or srcset attributes. This approach can prevent Google from discovering and indexing your images.
Splitt warned: “We’ve seen multiple lazy loading libraries that use some sort of data-source attribute rather than the source attribute. If it’s not in the source attribute, we won’t pick it up if it’s in some custom attribute.”
How to Audit Your Lazy Loading Implementation
Want to verify your images are properly configured for both performance and SEO? Follow these steps:
Use Search Console’s URL Inspection Tool:
- Navigate to the specific page you want to check
- Click “View tested page” to see rendered HTML
- Examine the source code rather than relying on screenshots
- Confirm image URLs appear in standard
srcandsrcsetattributes
Check Your Above-the-Fold Content:
- Identify your hero images and primary visual elements
- Ensure these don’t have
loading="lazy"attributes - Verify width and height dimensions are specified
- Test loading performance on slower network connections
As Splitt advised: “If the rendered HTML looks like it contains all the image URLs in the source attribute of an image tag, then you will be fine.”
The Real Ranking Impact
While Core Web Vitals do influence search rankings, Splitt provided perspective on the actual impact. He described it as “a tiny minute factor in most cases.”
However, the user experience implications extend far beyond search rankings. Poor LCP scores correlate with:
- Higher bounce rates
- Reduced user engagement
- Lower conversion rates
- Decreased perceived site quality
Best Practices for Strategic Lazy Loading
Ready to optimize your lazy loading strategy? Here’s your action plan:
For Above-the-Fold Content:
- Keep hero images and critical visuals eager-loaded
- Always include width and height attributes
- Prioritize elements that contribute to LCP
- Test on various devices and network speeds
For Below-the-Fold Content:
- Use native
loading="lazy"for images and iframes - Apply lazy loading to non-critical visual elements
- Consider user scroll patterns and behavior
- Monitor performance impacts over time
Library and Custom Implementation:
- Migrate from JavaScript libraries to native attributes when possible
- Ensure final markup uses standard image attributes
- Validate implementation through rendered HTML inspection
- Test SEO visibility through Search Console
Moving Forward with Performance Optimization
Lazy loading remains a valuable performance optimization technique when applied thoughtfully. The key lies in selective implementation rather than blanket application across all images.
Focus on treating lazy loading as an opt-in feature for non-critical content below the fold. Your above-the-fold hero images, logos, and primary visual elements should load eagerly to maintain optimal LCP scores.
Regular monitoring through Search Console and performance testing tools will help you track the effectiveness of your lazy loading strategy. Remember, the goal isn’t just faster loading – it’s creating a seamless user experience that keeps visitors engaged with your content.
By understanding these nuances of lazy loading implementation, you can harness its benefits while avoiding the common pitfalls that harm your site’s Core Web Vitals performance. The difference between strategic and indiscriminate lazy loading often determines whether this optimization helps or hurts your overall site performance.
