Render-Blocking Resources
Checks for CSS/JS in the <head> that blocks first paint.
What this check measures
We list every <script> and <link rel="stylesheet"> in <head> without async/defer. Each blocks the browser from painting until loaded and parsed.
Why it matters
Render-blocking resources are the most common LCP killer. 3-5 synchronous third-party scripts in the head can add 2-3 seconds to LCP on mobile.
How our audit detects it
Parse <head>, find <script> without async/defer and <link rel="stylesheet"> without media=print. Report each.
Typical findings
- error_outlinejQuery loaded synchronously in head.
- error_outlineAnalytics script blocking without async.
- error_outline5 stylesheets loaded synchronously — only critical-path should be.
How to fix
Add `async` to non-critical scripts, `defer` to scripts that must run after parse. For CSS, inline critical CSS and load the rest with `media="print"` + JS swap trick.
Frequently asked questions
async or defer for analytics?expand_more
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