Performance Tools

Render-Blocking Resources Checker

Check a page for render-blocking stylesheets and scripts in its <head> that could be slowing down first paint.

Enter a URL to check its <head> for render-blocking stylesheets and scripts that could be slowing down how fast your page first appears.

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What Are Render-Blocking Resources?

Stylesheets and scripts in the page's <head> make the browser wait before showing anything. This tool lists the stylesheets and the scripts without async or defer in the head of a page.

When to Use It

When PageSpeed Insights reports "Eliminate render-blocking resources".
When pages show a blank screen for too long.

How to Use It

Enter the URL.
Review the blocking stylesheets and scripts.

Understanding the Result

Add defer to scripts that do not need to run before the page appears. Keep critical CSS small, and load non-essential styles later.

Limitations

Some stylesheets must block rendering to avoid unstyled content - the goal is to keep them few and small, not to remove them all.

Frequently Asked Questions

A CSS or JavaScript file loaded in a way that forces the browser to wait for it before it can display anything on screen - stylesheets without a restrictive media query, and scripts without async or defer, are the most common causes.

Add the async or defer attribute to your <script> tags - async loads the script in parallel and runs it as soon as it's ready, while defer runs it after the page has parsed, in order.

For CSS that's not needed immediately (like print styles), add a specific media attribute (e.g. media="print"). For critical CSS, consider inlining just what's needed for the initial view.