UnoCSS is an atomic CSS engine and utility-first framework that generates styles on-demand based on the specific classes used in your source code. By scanning your project files during the build process, it produces only the CSS necessary for your application, effectively minimizing bundle size and eliminating unused styles.
The engine distinguishes itself through a highly modular, configuration-driven architecture that allows for deep customization of design tokens, rules, and presets. It supports advanced styling patterns such as attribute-based styling, tag-based styling, and dynamic variant generation, enabling developers to define complex design systems that integrate directly into their existing build pipelines.
Beyond core generation, the project provides a comprehensive suite of tools for managing CSS output, including virtual layering for specificity control, responsive breakpoint configuration, and automated source code transformations. It also features robust developer experience enhancements, such as real-time IDE autocompletion, visual documentation previews, and interactive testing environments, to streamline the styling workflow.
The project is designed to integrate into standard frontend build pipelines and includes extensive support for component-based frameworks. It is distributed as a TypeScript-based library with documentation and tooling available for immediate project integration.
