E-commerce Web Performance Expert

Every second of loading costs you sales

Google and SOASTA measured the impact: one extra second of load time means 7% fewer conversions. On an e-commerce site doing €500k in monthly revenue, that's €35,000 lost every month. The math is simple, yet most sites I audit have an LCP over 3 seconds on mobile.

I'm Paul Delcloy, an independent web performance consultant for over 8 years. I optimize e-commerce sites of all sizes — from pure players to marketplaces, from B2C to B2B. My goal: make sure every product page, every listing, every checkout loads fast enough not to lose the visitor.

The e-commerce sites I've optimized

I've worked on the performance of CHANEL, DIOR, Jimmy Fairly, Decathlon, and many more. What's striking? Every stack is different. Between Shopify, PrestaShop, WooCommerce, Magento, SFCC, or even custom solutions. Despite a very wide range of technologies, the performance problems themselves are often similar.

Listing pages with more than 80 products that load all images at once. Faceted filters that trigger a full DOM re-render. Checkouts that ship dozens of JavaScript files or take several seconds to respond on the server side. These are the precise pain points I target first.

Where the milliseconds that matter are won

Product pages: it's the most visited and most conversion-critical page. LCP is often the main product image — if it takes 3 seconds to appear, the visitor is already gone. The job of a webperf expert is to prioritize the hero image on PDPs so it renders as quickly as possible. Banners or A/B tests that pop in abruptly? Your customers lose their reading flow, or click a different button than intended, and end up frustrated.

**Checkout ** : a slow or janky payment funnel kills trust. JavaScript Long Tasks during form entry degrade INP and create the impression of a broken site, hurting your brand. You must ensure this step — the one that causes the most abandonments — is perfect from a user-experience standpoint. A flawless UX strengthens brand perception, but its main business impact is to reassure customers.

**Category pages ** : lazy loading isn't enough when you have 200 products per page. You need a pagination strategy, or infinite scroll that doesn't destroy performance, accessibility, or SEO — DOM virtualization, progressive loading, and careful browser memory management are watchwords in the work of an e-commerce web performance expert.

Revenue Impact Calculator

Estimate your monthly gain after web performance optimization

Visitors / month 50 000

Conversion rate 2.5%

Average basket $85

Current revenue / month

$0

Revenue after optimization

$0

+0.5% conversion

Estimated gain / month

$0

Source: WPO Stats ↗ — Correlation studies between web performance and conversion rates

The measurable business impact

Core Web Vitals aren't just a Google ranking factor — they reflect real user experience. When LCP drops from 4 seconds to 1.8 seconds, bounce rate mechanically goes down. When INP drops below 200 ms, users interact more with filters, product configurators, the cart. When CLS approaches 0, dead clicks and frustration fall sharply.

On the e-commerce sites I've optimized, the pattern is consistent: Core Web Vitals turn green in CrUX, conversion rate improves, and acquisition cost goes down because Google Ads rewards fast landing pages via Quality Score.