Shopify iframe loading attributes and the Core Web Vitals

Sites with default eager iframe loading have a good LCP most often: 94%, against 95% of all Shopify sites. Sites with loading="lazy" iframe loading have it least often, at 94%.

Sites with loading="lazy" iframe loading have a good INP most often: 94%, against 93% of all Shopify sites. Sites with default eager iframe loading have it least often, at 92%.

Default eager is the most used: 99.0% of Shopify sites.

Across the four LCP sub-parts in Chrome's field data, the largest gap between default eager and loading="lazy" sits in element render delay: 324 ms median for default eager against 281 ms for loading="lazy". Overall median field LCP is 1.4s for default eager (TTFB 406 ms, load delay 603 ms, load duration 205 ms, render delay 324 ms) versus 1.3s for loading="lazy".

Across the four LCP sub-parts in Chrome's field data, the largest gap between default eager and loading="lazy" sits in element render delay: 324 ms median for default eager against 281 ms for loading="lazy". Overall median field LCP is 1.4s for default eager (TTFB 406 ms, load delay 603 ms, load duration 205 ms, render delay 324 ms) versus 1.3s for loading="lazy".

jQuery sets the iframe loading to default eager on 99% of its sites, and 93% of jQuery sites have a good LCP, against 95% of all sites.

jQuery sets the iframe loading to default eager on 99% of its sites, and 92% of jQuery sites have a good INP, against 93% of all sites.

FrameworkIframe loading on its sitesGood LCP

Shopify sites with iframe loading 6,485 sitesDefault eager iframe (no loading="lazy") 99%95%

Vue 753 sitesDefault eager iframe (no loading="lazy") 99%94%

jQuery 2,638 sitesDefault eager iframe (no loading="lazy") 99%93%

Default eager iframe (no loading="lazy") Lazy-loaded iframe (loading="lazy")

Does the framework explain the iframe loading difference?

On jQuery, 92% of sites with default eager iframe loading have a good LCP, against 89% of jQuery sites with loading="lazy". Within jQuery, sites with default eager and loading="lazy" have a good LCP about equally often.

On jQuery, 92% of sites with loading="lazy" iframe loading have a good INP, against 92% of jQuery sites with default eager. Within jQuery, sites with loading="lazy" and default eager have a good INP about equally often.

How embedded iframes compete for network and main-thread budget

Every eager iframe initializes a nested browsing context that fetches its own HTML, stylesheets, and scripts during page startup. Among iframe-using sites, 99.0% include default eager iframes (94% good LCP, 1.4s median LCP) - often lightweight analytics or payment sandboxes - while 3.8% use loading="lazy" (94% good LCP, 1.3s median LCP), predominantly on article pages embedding heavy video players or maps.