Lazy Loading & Image Optimization
TL;DR
Lazy loading defers off-screen images until needed, cutting initial load time. Combined with WebP/AVIF formats, it can slash page weight by 50%+.
Explain Simply
Lazy loading is like a waiter who only brings your food when you're ready to eat, instead of piling everything on the table at once. Your page loads the images you can see first, and fetches the rest as you scroll.
Lazy loading defers image loading until they approach the viewport, improving initial load speed. HTML native: loading="lazy". Related: srcset for responsive images, WebP/AVIF for modern formats 25-50% smaller.
Native lazy loading (loading="lazy") is supported by all modern browsers and requires no JavaScript. However, above-the-fold images — especially the LCP element — should NOT be lazy-loaded, as this delays the largest visible content.
Image optimization goes beyond lazy loading: use srcset and sizes attributes for responsive images (serve appropriate sizes per device), convert to WebP (25-35% smaller than JPEG) or AVIF (50% smaller), compress appropriately (80-85% quality is usually indistinguishable), and always specify width/height to prevent CLS.
⚡Why It Matters
Images often account for 50%+ of page weight. Lazy loading improves LCP for image-heavy pages. WebP is 25-35% smaller than JPEG, AVIF is 50% smaller. Proper image optimization alone can improve PageSpeed scores by 20-30 points.
🔍How AiSEO Checks
AiSEO checks loading="lazy" on below-fold images, srcset for responsive, format (prefers WebP/AVIF), width/height to prevent CLS, and alt text for accessibility.
AiSEO Score Impact
Up to 2 points in the Performance category (15% of total score)
Fix Difficulty
Editor: Easy | Developer: Easy | AI Agent: Easy