A preprocessor is a tool that extends the capabilities of CSS by adding extra features and functionality. It is a file with the code that is compiled into CSS. Preprocessors suggest various features, including variables, nesting, functions, mixins, etc.

Some popular preprocessor languages for CSS include Sass, Less, and Stylus. These preprocessor languages are designed to make CSS more efficient and easier to work with and are used by many developers for large-scale projects.

There is no significant difference between all of them. The main concept is the same so we will consider all advantages of preprocessors in the example of sass.

Advantages

• Project structuring - We can write code in different files and folders that make the structure clean and predictive;
• Functionality - We can write code more manageable and more efficiently due to the additional preprocessor functionality;
• Compatibility - sass syntax is fully compatible with existing css rules, allowing ready-to-use css code to be included in a sass file, not vice versa.

Disadvantages

• Syntax - We need to spend time learning the syntax and get used to the extra functionality;
• Compilation - We need to conduct one more step is to convert sass into css.