js-beautify is a production-grade code formatter for JavaScript, CSS, and HTML, available as both a Node.js library/CLI and a Python package. The core architecture is a tokenizer-pipeline: source text is scanned by an InputScanner, tokenized by language-specific tokenizers (JavaScript, CSS, HTML), and then processed by a Beautifier that manages indentation, line wrapping, brace styles, and operator positioning via a stateful flag system. The Output class provides efficient indentation caching and wrap-point management. The tool supports a wide range of configuration options (indent size, brace style, attribute wrapping, template languages) and includes built-in unpackers for obfuscated scripts (P.A.C.K.E.R, JavascriptObfuscator, etc.). A web interface is also provided, built with CodeMirror and RequireJS. The project maintains near-identical JavaScript and Python implementations, sharing test data generated from Mustache templates to ensure parity. The codebase is well-structured with clear separation of concerns (core, language-specific, CLI, web), extensive test coverage (including regression tests for hundreds of GitHub issues), and a mature build/release pipeline. However, the dual-codebase requirement increases maintenance burden, and some parts (e.g., the web UI, Debian packaging) show signs of drift. The large test data files and complex matrix-based test generation add brittleness.