Performance Tools

Render-Blocking Resources Checker

Find the CSS and JavaScript files that make browsers wait before showing a page.

Not sure what to enter? Try an example: wordpress.org

Free & instant No signup How to use FAQ

Enter a URL to list the stylesheets and scripts in its head that block rendering, so you know which to defer or load differently.

What are render-blocking resources?

Stylesheets and scripts in a page's <head> that the browser must download and process before it can show anything are render-blocking. Too many of them delay the first paint. This checker lists the blocking CSS and JavaScript it finds in the head.

How to find render-blocking resources

Enter the domain or URL in the box above.
Click Check Resources.
Review the blocking stylesheets and scripts.
Add defer or async to scripts that are not needed immediately, and inline only the critical CSS.

Related checks

To shrink scripts, use the JavaScript Minifier.
To check images too, use the Image Optimization Checker.

Add defer to scripts that are not needed for the first screen and inline only the small amount of CSS above the fold. JustChecker tracks load times so you can see whether the page gets faster.

Frequently Asked Questions

A normal script tag in the head stops the browser until it has downloaded and run the file. Adding defer or async lets the page keep rendering meanwhile.

Critical CSS needed for the top of the page can be inlined; the rest can be loaded with media attributes or after the page renders. Many caching plugins automate this.

Indirectly - they delay First Contentful and Largest Contentful Paint, which are part of Google's Core Web Vitals.

Share this tool:

Need a website for your business? Only $599