P2 · MediumPerformance

Render-blocking JS

Scripts blocking page render

Code: render_blocking_js

Why it matters

Scripts blocking page render. Slow experiences increase bounce rates and hurt Core Web Vitals scores. Google uses these metrics as a direct ranking signal.

How to fix

Defer non-critical scripts

html

<!-- Before -->
<script src="/heavy-script.js"></script>

<!-- After -->
<script src="/heavy-script.js" defer></script>

Related checks in Performance

Slow First Contentful Paint

FCP exceeds 3 seconds

FCP needs improvement

FCP between 1.8-3 seconds

Slow Largest Contentful Paint

LCP exceeds 4 seconds

LCP needs improvement

LCP between 2.5-4 seconds

Poor Cumulative Layout Shift

CLS exceeds 0.25

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