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A CSS preprocessor with variables, mixins, and functions. Similar to SCSS with a slightly different syntax.
LESS (Leaner Style Sheets) is a CSS preprocessor created by Alexis Sellier in 2009, later maintained by the open-source community. Inspired by Sass, LESS introduces variables, mixins, nested rules, mathematical operations, and functions while using a syntax closely resembling standard CSS. It can run both server-side via Node.js and client-side in the browser, a unique capability that simplified early adoption.
LESS gained widespread popularity as the original styling language of Bootstrap (versions 2 and 3) and remains the preprocessor of choice for Ant Design, one of the most popular React UI libraries globally. Enterprise applications built with these frameworks often maintain extensive LESS codebases for theme customization and component styling. The LESS ecosystem includes the lessc compiler, integration plugins for Webpack and Gulp, and editor support across VS Code, WebStorm, and Sublime Text.
Key features include lazy evaluation of variables, mixin guards for conditional logic, and the ability to use JavaScript expressions within stylesheets. While Bootstrap migrated to Sass in version 4 and native CSS has adopted features like custom properties, LESS maintains relevance through its massive installed base, particularly in enterprise environments and Chinese tech ecosystems where Ant Design dominates. The language continues to receive maintenance updates and remains fully functional for modern web development workflows.
LESS variable changes and mixin overrides can ripple through an entire theme, making diffs essential before compiling. Modifications to lazy-evaluated variables may produce different results depending on scope context.
Comparing LESS files is critical when customizing framework themes like Ant Design, where a single variable file controls hundreds of component styles. Teams must catch accidental guard condition changes and import order shifts that alter the final CSS output.
UtraDiff compares LESS files with LESS syntax highlighting, covering variables, mixins, guards, and namespace scoping. Side-by-side view aligns mixin definitions and nested selectors across panels. The whitespace ignore toggle handles indentation changes from refactored nesting depth.
Alt+Arrow navigation jumps between modified rules. Language-aware tokenization distinguishes variable references (@var) from media queries (@media), preventing false matches in stylesheet restructuring diffs.
Supported extensions: .less