Core Web Vitals are no longer a niche topic for developers. Since Google made them a direct ranking factor, a 4-second LCP or a jumping CLS costs positions on product queries — and therefore revenue. In 2026, INP has replaced FID and tightens the screws further on mobile. The good news: a PrestaShop store can get into the green without a rebuild, provided you tackle the three metrics in the right order.
This article details the complete optimization chain: what really weighs on LCP, INP and CLS, and the technical levers that flip the Search Console status from “Needs improvement” to “Good”.
Understanding what each metric measures
LCP (Largest Contentful Paint) measures how long the largest visible element takes to render — often the main product image or the home hero visual. INP (Interaction to Next Paint) measures responsiveness: the delay between a click and the page’s visible response, dragged down by JavaScript. CLS (Cumulative Layout Shift) measures visual stability: any element that “pushes” content after the fact (an image without dimensions, an injected banner) degrades the score.
Step 1 — Full-page cache, the biggest LCP lever
PrestaShop regenerates the HTML on every visit if nothing caches it. On shared hosting, the TTFB (time to first byte) explodes and pulls the LCP up. A full-page cache serves the already-built HTML in a few milliseconds. It is, by far, the lever with the most impact on LCP — before you even touch the images. Combined with Critical CSS generation (the minimal CSS needed to render above-the-fold, injected inline, the rest loaded deferred), you remove the render-blocking that delays first paint.
That is exactly what a dedicated PrestaShop performance pack bundles: page cache, Critical CSS and advanced optimizations in a single module, with no server tinkering.
Full Page Cache & Speed Optimization for PrestaShop 8 & 9Page cache, Critical CSS and advanced optimization for PrestaShop 8 and 9.€149.00
Step 2 — Next-gen images (WebP / AVIF)
On a store, images often account for 70% of page weight. Serving JPEG/PNG in 2026 leaves 30 to 60% of unnecessary weight on the table. WebP, and especially AVIF, deliver the same visual quality for a fraction of the weight — a direct gain on mobile LCP. The rule: automatic on-the-fly conversion, served locally (no dependency on a paid third-party CDN), and a fallback for older browsers.
On PrestaShop, the WebP & AVIF image optimizer performs this conversion automatically and 100% locally. If your store runs on WooCommerce, the equivalent is WebP AVIF Pro — same logic, no subscription.
Step 3 — Mastering CLS and INP
CLS is fixed by reserving space: explicit dimensions or aspect-ratio on every image and iframe, fonts loaded with font-display swap and a metric fallback. INP is won by lightening the JavaScript: deferring non-critical scripts, avoiding heavy sliders and popups at load. A classic case that hurts both: a poorly integrated product gallery or video — a topic we detailed in our analysis of product video vs Core Web Vitals.
The special case of faceted pages
Filtered category pages (faceted search) are often the worst offenders: full reloads, non-indexable URLs, heavy JavaScript. A faceted engine designed for performance and SEO, such as faceted search & SEO for PrestaShop, resolves filters server-side with indexable landing pages and fast rendering — instead of degrading INP on every filter click.
Conclusion: optimize in order, measure continuously
The winning sequence is clear: full-page cache and Critical CSS first (maximum LCP impact), then next-gen images, then stability (CLS) and responsiveness (INP). Measure before/after in Search Console on field data (CrUX), not just in lab Lighthouse. To dig into the method with real code, our 2026 Core Web Vitals checklist with PHP and SQL goes further, and all our guides are gathered in the category Performance and Core Web VitalsPerformance and Core Web Vitals optimisation: LCP, CLS, INP, native and advanced lazy loading, image conversion to WebP / AVIF, CDN, critical CSS generation, browser and server cache, font optimisation,…