JavaScript Defer Checker
A script without defer or async stops the browser from showing the page until it is loaded. The tool lists the scripts of a page that block rendering.
Checked by our server, free and without an account
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What the tool looks at
- External scripts without defer or async.
- How many scripts the page loads in total.
How it works
- Enter the address. Only public web addresses on the standard ports are accepted.
- Our server fetches what the check needs once, with its own honest bot name, and evaluates it.
- You get the evaluated values with a short explanation. Nothing from the page is stored.
More Performance tools
All tools- TTFB CheckerMeasure the time to first byte of a page – how quickly the server starts to answer.
- Page Size CheckerCheck how large the HTML of a page is – transfer size and uncompressed size, with a rating.
- DOM Size CheckerCount the HTML elements of a page – a large DOM makes rendering and interaction slower.
- HTTP/2 CheckerCheck whether a website is served over HTTP/2 – faster loading of many files over one connection.
- Compression CheckerCheck whether a server compresses its pages – Gzip, Brotli or Zstandard, or none at all.
- Brotli CheckerCheck whether a server supports Brotli compression – usually smaller than Gzip for text files.
- HTTP Requests CheckerCount the scripts, stylesheets, images and other files a page loads – fewer requests load faster.
- Image Format CheckerCheck whether the images of a page use modern formats such as WebP or AVIF instead of large JPEG and PNG files.
- Lazy Loading CheckerCheck whether the images of a page are lazy loaded – images further down only load when they are needed.
The whole page in one audit
One audit runs more than 50 tests, rates them by severity and turns them into a score. Websites are re-checked on a schedule.