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PERF007 · Render-blocking script

Severity: warning

What it checks

Section titled “What it checks”

Flags a <script src> in <head> that has neither defer, async, nor type="module" — whether authored in src/app.html (caught in rendered analysis) or in <svelte:head> (caught in static analysis). A head with no <script> is not checked.

Why it matters

Section titled “Why it matters”

A synchronous <script src> in <head> blocks HTML parsing until it downloads and runs, delaying first paint. defer, async, or type="module" avoids the block. SvelteKit’s own scripts are already module/deferred — this catches hand-added blocking scripts.

How to fix

Section titled “How to fix”

Add defer (or type="module") / async:

src/app.html
<script src="/analytics.js" defer></script>