CLI application for validating generated critical CSS

Usage no npm install needed!

<script type="module">
  import criticalCli from '';



critical-cli is a CLI tool for validating critical CSS on a certain website.

Basically the website is loaded without stylesheets at first and compared against a version with loaded stylesheets. If the generated screenshots do not match the critical CSS on the page is considered as incorrect. The tool will show the difference in percent on the standard output


npm i critical-cli --save-dev


The CLI application provides a run command to validate critical CSS:

critical-cli run --url

If the critical CSS validation for the page fails the application will immediately exit with an exit code of 1. All remaining URLs will not be checked.


The following configuration options can be passed to the run command.

Option Default Description
url N/A the URL(s) to check
output ./reports output path for page screenshots
generateReport true flag to generate html report with test output
width 1024 viewport width used for critical CSS comparison
height 768 viewport height used for critical CSS comparison
timeout 1000 timeout in milliseconds for loading stylesheets
cleanup false flag to cleanup output folder before run
stopOnFailure true flag to stop on first failure
verbose false flag to set verbose output


critical-cli run --url --output ./other-dir --width 1920 --height 1080 --timeout 5000

Configuration with JSON

By passing the --config <filename> option you can define your command parameters in a JSON file. This JSON file can contain all valid cli options.

Example JSON:

    "url": [
    "width": 1920,
    "height": 1080


critical-cli run --config critical.json


The CLI generates a screenshot of the website with its critical CSS and a screenshot with all stylesheets loaded, also a diff image is generated.

Critical Version Normal Version Diff

This makes it easy to determine the problems with your critical CSS.


To be able to review the output in an easy way the CLI by default generates an HTML report containing information about the last test results.


The MIT License (MIT). Please see the License File for more information.