By Shad Super in Questions —

How Can I Optimize My Website's Resource Hints Like Preload, Prefetch, and DNS-Prefetch to Improve Core Web Vitals Scores?

Summary

Optimizing a website's resource hints such as preload, prefetch, and dns-prefetch can improve Core Web Vitals scores, which are important metrics for user experience quality. This involves understanding each of the resource hints, appropriately implementing them, and also monitoring their effect on your website's performance.

Understanding Resource Hints

Preload

The `<link rel="preload">` hint is used for fetching resources that you believe the page will need soon, but that are not needed to initially display the content. It can be used to load important resources early, and as a result potentially improving the overall page load time [Preload Resources, Google Web Fundamentals].

Prefetch

The `<link rel="prefetch">` hint is used to fetch resources that might be needed for future navigation. By prefetching these resources during idle time, subsequent page loads can be made faster [Prefetching, Preloading, Prerendering, Google Web Updates].

DNS-Prefetch

The `<link rel="dns-prefetch">` hint is used to resolve domain names before the resources are needed, thus saving time when those resources are requested [X-DNS-Prefetch-Control, MDN Web Docs].

Implementing Resource Hints

Resource hints can be used in a variety of ways to boost page load performance. Here are some implementation guidelines for each of the resource hints.

Preload

Use `<link rel="preload">` for resources that are needed in the current navigation. This can be particularly useful for loading Web Fonts, important scripts, and critical CSS files [Optimize CSS Delivery with preload, web.dev].

Prefetch

Use `<link rel="prefetch">` for resources that might be needed in the next navigation. This can be useful for fetching resources for subsequent pages that a user is likely to visit in the current session [Link Prefetch, web.dev].

DNS-Prefetch

Use `<link rel="dns-prefetch">` for resources hosted on different domains. This can help save network latency when those resources are requested [Preconnect and DNS-Prefetch, web.dev].

Monitoring Performance

After applying resource hints, monitor the impact on performance metrics such as Largest Contentful Paint (LCP) and First Input Delay (FID). You can use Google's Lighthouse, and WebPageTest for this purpose.

Final Thoughts

Optimizing resource hints can significantly improve your website’s Core Web Vitals scores. However, their use should be tailored on a case-by-case basis. Always test the impact of hints on your website's performance before and after their implementation.

References