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Render Blocking Resources Checker

Find the scripts and stylesheets in your head that delay first paint.

Free, no signup. We fetch the page once and read what your server sends back.

Fetching the page…

What this checks

A script or stylesheet in the head with no async or defer stops the browser drawing anything until it has downloaded and run. On a slow connection that is the difference between a page appearing in one second and in five.

  • Blocking stylesheets in the head
  • Blocking scripts in the head
  • Total blocking resources

How to act on the result

  • Add defer to scripts that do not need to run before render. That is nearly all of them.
  • Inline the small amount of CSS needed for the top of the page and load the rest asynchronously.
  • Third-party tag managers and font loaders are the usual offenders.

Frequently asked

What does render-blocking mean?

The browser cannot paint the page until the resource is fetched and processed. The user stares at a blank screen for that time.

Is CSS always render-blocking?

Stylesheets without a media attribute are, by design, because the browser needs styles before painting to avoid a flash of unstyled content.

What is the difference between async and defer?

Both download without blocking. async runs as soon as it arrives, possibly out of order. defer runs in order after HTML parsing. defer is the safer default.

Do web fonts block rendering?

The stylesheet that declares them does. The font files themselves block text painting depending on font-display. Using font-display: swap avoids invisible text.

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