CSS Minifier is an online tool that helps to minify or compress the CSS code to make it smaller and more optimized. It removes unnecessary whitespace, comments, and other characters from the CSS code, without affecting its functionality or layout. This reduces the file size, which improves the website's performance by reducing the page load time. CSS Minifier can also help to improve the code readability by formatting the code into a more structured and consistent style. With this tool, web developers can easily optimize their CSS code, which helps to enhance the user experience and improve the website's overall performance.