Lazy loading is a web performance technique that delays loading non-critical page elements, such as below-the-fold images, videos, or embedded content, until a user is about to see them. Instead of loading everything at once, the browser loads the most important content first, which can improve page speed, reduce initial page weight, and create a better user experience.
Why lazy loading matters for SEO and UX
Lazy loading matters because faster-loading pages are easier for users to interact with and more efficient for search engines to crawl. When a page loads too many large assets upfront, it can slow down rendering, increase bandwidth use, and hurt important performance signals such as Largest Contentful Paint. For ecommerce sites, blogs, and service pages with many images, this can affect engagement and conversions.
Used correctly, lazy loading helps prioritize above-the-fold content so visitors can start reading or shopping sooner. It is especially useful on mobile, where slower connections and limited data make heavy pages more frustrating.
How lazy loading works
The browser loads essential content first, including text, layout, and visible media. Assets farther down the page are deferred until the user scrolls near them. Many modern browsers support native lazy loading for images and iframes, which makes implementation simpler for site owners and developers.
What should be lazy loaded
Good candidates include gallery images, blog post images that appear later on the page, video embeds, product recommendation widgets, and review sections. These elements are useful, but they do not need to load before the visitor sees the top of the page.
What should not be lazy loaded
Do not lazy load critical above-the-fold images, your main hero image, primary content needed for interaction, or important elements that search engines and users need immediately. If key content is delayed too aggressively, the page may feel broken or incomplete.
Practical example and best practices
Imagine a category page with 40 product images. Without lazy loading, the browser tries to load all 40 images immediately, even though the visitor only sees the first 6. With lazy loading, only the visible product images load first, while the rest load as the user scrolls. This can reduce initial load time and make the page feel faster.
Best practices include testing that images still appear correctly on mobile, keeping image dimensions defined to prevent layout shifts, and making sure important content is still accessible to users and crawlers. Lazy loading should support performance, not hide valuable content.