Connection and preload hints and the Core Web Vitals

Sites with no resource hints connection and preload hints have a good LCP most often: 89%, against 86% of all sites. Sites with only dns-prefetch hints connection hints have it least often, at 78%.

No resource hints is the most used: 41.8% of sites.

Across the four LCP sub-parts in Chrome's field data, the largest gap between no resource hints and only dns-prefetch hints sits in time to first byte (TTFB): 520 ms median for no resource hints against 938 ms for only dns-prefetch hints. Overall median field LCP is 1.3s for no resource hints (TTFB 520 ms, load delay 221 ms, load duration 93 ms, render delay 163 ms) versus 1.7s for only dns-prefetch hints.

Joomla sets the connection and preload hints to no resource hints on 90% of its sites, and 93% of Joomla sites have a good LCP, against 86% of all sites. Shopify sets the connection and preload hints to both preconnect and preload hints on 77% of its sites, and 97% of Shopify sites have a good LCP.

PlatformConnection and preload hints on its sitesGood LCP

Sites with connection and preload hints 201,622 sitesNo resource hints 42%Preload without preconnect 16%Preconnect without preload 16%DNS-prefetch only 14%Both preconnect and preload 13%86%

Shopify 8,573 sitesBoth preconnect and preload 77%Preconnect without preload 18%97%

Squarespace 2,258 sitesPreconnect without preload 98%94%

Drupal 3,296 sitesNo resource hints 76%93%

Joomla 2,551 sitesNo resource hints 90%93%

Wix 5,825 sitesPreload without preconnect 89%92%

Adobe Commerce 1,095 sitesNo resource hints 41%Preload without preconnect 34%Both preconnect and preload 14%Preconnect without preload 10%83%

WordPress 65,509 sitesDNS-prefetch only 35%No resource hints 23%Preload without preconnect 16%Preconnect without preload 16%Both preconnect and preload 10%76%

No resource hints Preload without preconnect Preconnect without preload DNS-prefetch only Both preconnect and preload

Does the platform explain the connection and preload hints difference?

On WordPress, 82% of sites with no resource hints connection and preload hints have a good LCP, against 77% of WordPress sites with preload hints without preconnect. Within WordPress, sites with no resource hints have a good LCP more often. On Shopify, 94% of sites with preload hints without preconnect connection and preload hints have a good LCP, against 95% of Shopify sites with preconnect hints without preload. Within Shopify, sites with preload hints without preconnect and preconnect hints without preload have a good LCP about equally often.

Why targeted preload and preconnect beat legacy dns-prefetch

dns-prefetch only resolves the domain name, leaving TCP and TLS handshakes on the critical path. Pairing preconnect on critical asset CDNs with preload on the LCP image eliminates both connection and discovery delay. Across 25,979 sites (12.9%) pairing preconnect and preload, 87% pass field LCP (1.4s median), compared with 78% (1.7s median) on the 13.6% using dns-prefetch alone.