WebMarkupMin is a comprehensive .NET library for minifying HTML, XHTML, XML, CSS, and JavaScript markup to optimize web application performance. It provides a core minification engine with parsers and output writers, plus extensive integration with ASP.NET (both classic .NET Framework and .NET Core/5+) through middleware, HTTP modules, MVC action filters, and WebForms base page classes. The library supports multiple minifier backends: built-in Crockford JS and Kristensen CSS minifiers, plus wrappers for Microsoft Ajax Minifier, YUI Compressor, and NUglify. It also includes compression support for GZip, Deflate, and Brotli. The architecture is modular, with clear interfaces (IMarkupMinifier, ICssMinifier, IJsMinifier, ICompressor) and factory patterns, enabling pluggable backends and easy extension. Configuration is exposed via strongly-typed settings classes. The codebase is well-tested with hundreds of unit tests covering edge cases in markup parsing, whitespace handling, attribute optimization, and framework-specific features (Angular, Knockout, Blazor). The repository is primarily a library (not a standalone application), and its samples demonstrate integration with various ASP.NET versions.