CSS tools are software applications or online platforms that help developers create and manage Cascading Style Sheets (CSS) more efficiently. These tools can include code editors, preprocessors, and frameworks that streamline the styling process, making it easier to design visually appealing websites. Popular examples include Sass, Less, and Bootstrap. Many CSS tools offer features like syntax highlighting, code completion, and live previews, which enhance productivity and reduce errors. Additionally, some tools provide built-in libraries of styles and components, allowing developers to quickly implement responsive designs without starting from scratch.