What Role Does Browser Resource Prioritization Play in Improving Core Web Vitals, and How Can I Ensure Efficient Resource Loading?


Browser resource prioritization is a key mechanism that improves Core Web Vitals by ensuring efficient loading of web resources. It does this by dictating the order in which resources are loaded, thereby enhancing metrics such as Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS). To ensure efficient resource loading, a variety of optimization strategies can be employed, including preloading, preconnecting, and prefetching, as well as HTTP/2 Server Push, and lazy loading.

Understanding Browser Resource Prioritization

When a browser loads a web page, it doesn't fetch and process all resources simultaneously. Instead, it prioritizes certain resources based on their relevance and immediacy to the user experience. This prioritization crucially influences Core Web Vitals. By efficiently managing resource loading, one can optimize for LCP, FID, and CLS.

Techniques for Efficient Resource Loading


Preloading assists the browser in determining which resources are critical to initial page loading and should be downloaded first. By adding `<link rel="preload">` to a document's head, it can prioritize critical resources above less important ones [Preload, 2019].


Preconnecting allows the browser to set up early connections before an HTTP request is dispatched. This can be done by adding `<link rel="preconnect">` to the head of the document, which can help speed up the delivery of assets from the chosen origin [Preconnect, 2019].


Prefetching is a technique where resources are loaded in advance while the browser is idle, preparing them for future navigation. Implementing prefetching is done using `<link rel="prefetch">`. It's best used for resources that might be needed for subsequent navigations [Prefetch, 2019].

HTTP/2 Server Push

HTTP/2 Server Push allows the server to send resources to the browser before they are explicitly requested. This can be beneficial for resources that the server knows the browser will need to render the page [HTTP/2 Server Push, 2019].

Lazy Loading

Lazy loading is a strategy where non-critical resources are loaded only when they are needed. This is particularly useful for images and iframes that aren't immediately visible on page load. By delaying the load of these resources, it allows critical resources to load more quickly [Native Lazy Loading, 2020].


Efficiently managing resource prioritization can significantly enhance Core Web Vitals, leading to a better user experience. By implementing the techniques outlined, developers can ensure the optimal loading of resources on a web page.