PrettyCSS is more than just a CSS pretty printer. Deep down, it tokenizes and parses your CSS file like how a browser would load it. The structure of the CSS is checked for errors, the property names are checked and the values are validated to make sure they are potentially valid for that specific property.
Here is a list of the types of problems that are detected:
The goal of the project is to create a single command-line tool that can read any of the CSS files that we use at work and write it out reformatted. The user should have the ability to specify any of the whitespace that gets modified anywhere in the file as well as determine what version of CSS that is being targeted. To help prevent against mistakes, property names and values are checked. In the end, this tool would be integrated with our development environment, so every commit to a CSS file would get standardized and checked before it entered our codebase.