Case study
Shopify Plus LCP: 4.2s → 1.1s
A high-traffic Shopify Plus store was losing conversions to slow mobile load times. LCP sat at 4.2s on key product pages.
Problem
The hero image loaded at full resolution with no priority hints. Third-party app scripts blocked rendering in the `<head>`. Theme CSS included unused rules from deprecated sections, inflating render time. Mobile scores were failing Core Web Vitals thresholds.
Fix
Audited the theme Liquid and identified the LCP element. Added `fetchpriority="high"` and responsive `srcset` on the hero image. Deferred non-critical app scripts to after first paint. Inlined critical above-the-fold CSS and removed 40KB of dead theme styles. Configured lazy-loading for below-fold product grids.
Stack
- Shopify Plus
- Liquid
- JavaScript
- Theme Kit
Turnaround
Same-day (6 hours)
Outcome
LCP dropped from 4.2s to 1.1s on mobile product pages. CLS held at 0.02. The client passed Core Web Vitals assessment within 48 hours of deployment.
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