Shopify LCP image loading and the Core Web Vitals

Sites with loading="lazy" have a good LCP most often at 97%, followed by no loading attribute at 97% and loading="eager" at 95%. Within Shopify, default loading and loading="lazy" have a good LCP about equally often.

An <img> element is the Largest Contentful Paint element on 77.0% of audited Shopify sites, ahead of CSS background images (9.6%) and text blocks (8.7%). Among the 6,066 Shopify sites with an <img> LCP element, 46.0% omit the loading attribute, 31.2% set loading="lazy", and 22.8% set loading="eager".

Putting loading="lazy" on the LCP image raises median resource load delay from 569 ms to 587 ms in Chrome's field data. That is a 18 ms wait before the browser starts downloading the image. Without loading="lazy", Chrome's preload scanner queues the <img> as soon as it reads the HTML. With loading="lazy", Chrome holds the request back until layout confirms the image sits in the viewport. Sites with loading="eager" show a 571 ms load delay in the field because many of them also preload other assets or load the hero image from a script.

Adding fetchpriority="high" to a lazy-loaded LCP image does not fix the lazy-load delay. The 21 sites with both attributes still wait 773 ms before the image request starts, and 100% have a good LCP. In Chromium, ShouldDeferImageLoad runs before resource priority is assigned, so the request stays deferred until layout.

Vue puts loading="lazy" on the LCP image on 32% of its sites, and 95% of Vue sites have a good LCP. jQuery leaves the LCP image at the browser default on 54% of its sites and sets loading="lazy" on 29%, and 94% of jQuery sites have a good LCP.

FrameworkLCP image loading on its sitesGood LCP

Shopify sites with an <img> LCP element by loading attribute 6,066 sitesNo loading attribute (auto) 46%loading="lazy" 31%loading="eager" 23%96%

Vue 689 sitesNo loading attribute (auto) 42%loading="lazy" 32%loading="eager" 25%95%

jQuery 2,083 sitesNo loading attribute (auto) 54%loading="lazy" 29%loading="eager" 17%94%

No loading attribute (auto) loading="lazy" loading="eager"

Does the framework explain the loading="lazy" pass rate?

On jQuery, 94% of sites with default loading have a good LCP, against 95% of jQuery sites with loading="lazy" on the LCP image. Within jQuery, sites with default loading and loading="lazy" have a good LCP about equally often. On Vue, 95% of sites with default loading have a good LCP, against 97% of Vue sites with loading="lazy" on the LCP image. Within Vue, sites with default loading and loading="lazy" have a good LCP about equally often.

Why loading="lazy" holds back the preload scanner

Chrome's HTML preload scanner finds <img> tags in the first bytes of the document. It starts fetching default and eager images right away, before stylesheets and blocking scripts finish downloading. When an <img> carries loading="lazy", Chromium's ShouldDeferImageLoad check stops the preload scanner from queuing the request. The image waits until CSS downloads, the render tree builds, and layout confirms the image sits in the viewport. WordPress core has skipped loading="lazy" on the first three content images since version 6.3. Theme templates and page builders that hardcode loading="lazy" on hero banners still pay the full layout wait.