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A high-performance template engine with indentation-based syntax. Formerly known as Jade. Compiles to HTML.
Originally released in 2010 as Jade by TJ Holowaychuk, this template engine was renamed to Pug in 2016 due to a trademark dispute. Pug compiles indentation-based shorthand into HTML, eliminating the need for closing tags and angle brackets while providing a clean, whitespace-significant syntax that many developers find more readable than raw markup. The engine supports mixins for reusable components, template inheritance through extends and block declarations, conditional rendering, iteration, and inline JavaScript expressions.
Pug gained widespread adoption in the Node.js ecosystem as the default view engine for Express.js applications during the framework's early dominance of server-side JavaScript. It integrates with build tools like webpack and Gulp through dedicated loaders and plugins, and many static site generators and documentation tools support Pug as a templating option. The language includes a powerful filter system that allows embedding Markdown, CoffeeScript, and other languages directly within templates.
Pug's compilation step catches syntax errors before runtime, and its output can be configured for minified production HTML or pretty-printed development output. While newer approaches like JSX and server components have reduced Pug's market share in React-based projects, it remains actively maintained and popular in Express applications, legacy Node.js projects, and among developers who prefer separation of concerns between logic and markup. The concise syntax is particularly valued for email templates and server-rendered pages where component-based frameworks are overkill.
Pug's indentation-based syntax means that whitespace changes are structural, not cosmetic — a shifted block alters the HTML nesting hierarchy entirely. Comparing Pug files catches modified mixin signatures that break every call site, altered extends chains that restructure page layouts, changed conditional rendering logic that hides or exposes content, and reordered attributes that may affect CSS selectors.
Template designers reviewing layout updates need side-by-side comparison to verify that indentation shifts produce the intended DOM structure.
UtraDiff compares Pug template files with syntax highlighting that color-codes tag names, class/id shorthand, attributes, and embedded JavaScript expressions. Indentation-significant syntax gets full highlighting, making nesting changes clearly visible in the diff — a shifted line means a different parent element.
Side-by-side view separates structural nesting changes from attribute modifications. Alt+arrow navigation jumps between changed template blocks, and mixin definition changes stand out from mixin call-site updates.
Supported extensions: .pug .jade