Lazy loading, also called deferred loading, is a technique in web performance that delays the fetching of non-critical resources. Instead of loading all images, scripts, or videos when a page opens, the browser loads these elements only when they are about to come into view.

This helps reduce the initial page load time, saves mobile data, and improves overall site speed. For instance, images below the fold remain unloaded until the user scrolls near them. The opposite approach is called eager loading, where all content loads upfront.

How Lazy Load Helps Page Performance

Lazy loading helps web pages load faster by fetching only what is needed first. It avoids overloading the browser and improves overall speed, especially on mobile devices.

Faster page display

By loading only the visible part of a page first, lazy loading helps show usable content quickly. Off-screen images are skipped initially, which allows the top portion of the page to appear faster. This makes the first screen feel instant, improving the visitor’s first impression.

Reduced data usage

Lazy loading cuts down on data by avoiding downloads of unused images or videos. This reduces bandwidth for users and servers. When Wikipedia added lazy loading to mobile images, it saved about 450,000 GB of image data each year, which is roughly a 43 percent drop in image traffic.

Improved user experience

Pages using lazy loading feel quicker and smoother. Since fewer things load at once, the browser stays responsive. Users can start reading or clicking sooner, which lowers bounce rates and makes browsing feel more fluid.

Better performance scores

Deferring large items like below-the-fold images helps meet Core Web Vitals. For example, it can improve Largest Contentful Paint (LCP) by loading top images faster. Lazy loading also reduces main thread work, helping with Interaction to Next Paint (INP) by making pages react faster to clicks or scrolls.

SEO support

Lazy loading supports search engine performance when set up correctly. Since Google uses speed as a ranking factor, sites that load quickly often appear higher in search results. As long as the content is crawlable, lazy loading can help with both speed and search visibility.

How Lazy Load Is Implemented

Lazy loading works by loading content only when it becomes visible in the user’s screen area, known as the viewport. This section explains how developers apply lazy loading using HTML, JavaScript, and built-in platform tools.

Native HTML attribute

Most modern browsers support the loading=”lazy” attribute for <img> and <iframe> tags. This native lazy loading method is simple and widely used.

Example: <img src=”photo.jpg” alt=”Sample image” loading=”lazy”>

With this attribute, the browser delays loading the image until it is about to appear on screen. Content not marked with this tag follows the default rule, called eager loading, where items load as soon as the page starts.

Intersection Observer API

The Intersection Observer API uses JavaScript to check when an element comes near the viewport. When it does, the script swaps a placeholder with the real content, such as assigning the image’s src value.

This method works well for background images, sections with many components, or items that need precise control. Unlike scroll-based methods, it triggers loading automatically, without clicks or user input.

Third-party libraries and platform support

Before native support, many websites used tools like lazysizes, jQuery plugins, or custom scripts. Today, lazy loading is built into several platforms and frameworks:

• WordPress has enabled loading=”lazy” for images since version 5.5 (2020).
• Angular supports lazy loading of images and feature modules.
• Shopify themes and other CMS platforms often include built-in lazy load features.

These tools help developers use lazy loading without writing extra code.

Automatic triggers, not manual clicks

Lazy loading should always be automatic. It must rely on scroll-based or viewport-based detection, not on buttons or manual actions. Search engine crawlers like Google do not scroll or click. If content only loads after a user action, it may not be seen or indexed.

Proper lazy loading ensures content loads when it enters the viewport, even during crawler rendering. The native loading=”lazy” and Intersection Observer API both meet this standard.

Above-the-fold content should load eagerly

Elements that appear at the top of the page, known as above-the-fold content, should not be lazy-loaded. This includes the main banner image, hero text, or any large visual at the top. Delaying these elements can cause a blank area or poor first impression.

It can also hurt Core Web Vitals, especially Largest Contentful Paint (LCP), which measures how fast the main content appears. Best practice is to load top content eagerly and use lazy loading for below-the-fold resources or items that are not immediately needed.

How Lazy Load Affects Search Engines

Lazy loading does not block search engines if implemented correctly. Search crawlers like Googlebot can see lazy-loaded content as long as the page triggers loading automatically, without relying on manual user actions like clicks or scrolls.

Allow content to load without user action

Search engines do not scroll or interact with pages like users do. Lazy loading must happen as content enters the viewport. Methods like the native loading attribute (loading=”lazy”) or the Intersection Observer API load items at the right moment, without requiring clicks or key presses.

If lazy load depends only on scroll events, Googlebot may not see the content. For example, product details that load only when scrolled into view may never be indexed. Google recommends placing important content in the rendered HTML, so it is present even for crawlers that do not interact with the page.

Keep critical content visible

Avoid lazy loading any main content or navigation links. Pages should not delay loading product descriptions, headings, or banners that explain the page purpose. If these parts are not loaded early or visible in the DOM, search engines may skip them. To stay safe, load all essential text and primary visuals without delay.

Use unique URLs for infinite scroll

When lazy loading is used with infinite scroll, the extra content must still be reachable by crawlers. Google advises using separate URLs for paginated sections (like ?page=2, ?page=3). These URLs help search engines index every section.

If new items load on scroll, update the browser address using the History API and include proper internal links. This keeps user experience smooth while making sure bots can access all content. These URLs can be hidden or behind a “load more” button, as long as they exist in the HTML.

Prevent layout shifts

Lazy-loaded items like images can cause the page to move suddenly when they appear. This is called layout shift, and it affects the Cumulative Layout Shift (CLS) score in Core Web Vitals.

To avoid this, developers should set fixed width and height for every image, or use placeholders. This keeps the layout stable while the content loads. Platforms like WordPress version 5.5+ now add dimensions by default for this reason.

Verify content visibility to crawlers

After applying lazy loading, check that all content is visible to search engines. Use tools like Google Search Console or the URL Inspection Tool to see the page as Googlebot sees it. Make sure every lazy-loaded image or element shows up in the rendered HTML, with correct <img> and src attributes.

If content is missing, adjust the script or method. As long as the implementation meets Google’s guidelines, including no manual interaction, lazy loading will not block indexing.

History of Lazy Load

Lazy loading began as a software design pattern where objects were initialized only when needed. In web development, the idea gained attention as websites became more image-heavy and internet speeds varied across devices.

Early web usage

In the early 2000s, developers started writing custom JavaScript to delay image and module loading. Frameworks like Angular made this easier by supporting lazy loading of modules and images directly. This approach helped lower bandwidth usage, reduced page size, and improved load times.

In 2016, Wikimedia added lazy loading to mobile Wikipedia, cutting down around 14 percent of data per page and saving roughly 450 terabytes per year. These results showed clear performance benefits and encouraged broader adoption.

Native browser support

A major shift came in 2019, when Google Chrome introduced support for the loading=”lazy” attribute. By 2020, all major browsers enabled native lazy loading for images and iframes. This allowed developers to lazy load content using just HTML, without needing extra scripts.

Shortly after, WordPress version 5.5 began adding the loading=”lazy” attribute automatically to images in posts. This change improved speeds on millions of websites by reducing unnecessary data loads.

Other CMS platforms and website builders also integrated the feature as a default or simple setting.

Adoption driven by SEO and performance updates

Search engines started giving higher visibility to faster websites. In 2018, Google released the Speed Update, making page speed a ranking factor for mobile search. In 2021, the Page Experience update introduced Core Web Vitals into search algorithms.

As a result, lazy loading became part of standard performance practice. Google’s own tools, like PageSpeed Insights, recommend it under audits such as “Defer offscreen images”.

By 2025, lazy loading is widely used on content-rich sites including news portals, e-commerce stores, and media platforms. It is now viewed as a basic technique to build fast, efficient, and content-rich pages without compromising user experience.