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Speed High impact Medium 30–60 min

Render-blocking resources

CSS and JS in the head that delay the first render.

What it is

Render-blocking resources are files (typically CSS and synchronous JS in <head>) that the browser must download and process before it renders content. Until then the user sees nothing.

Why it matters

They are the most common cause of a slow first render and poor LCP. The more there are and the larger they are, the longer it takes for content to appear.

How to do it

  1. 1Defer scripts via defer/async.
  2. 2Identify "critical CSS" (styles for the visible part) and inline it, loading the rest asynchronously.
  3. 3Combine and minify CSS/JS files, remove unused styles.
  4. 4Load external fonts with font-display: swap and preload them.

Conclusion

The goal is to deliver visible content as early as possible and defer everything else. Start by deferring scripts (a quick win) and optimizing CSS (critical CSS). This area has a direct impact on LCP — a metric Google tracks.

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