Pug (formerly Jade) is a whitespace-sensitive HTML template language. Instead of angle brackets you write tag names with attributes in parentheses and nest children using indentation. It compiles to standard HTML.
In Pug, .foo is shorthand for div(class="foo") and #bar is shorthand for div(id="bar"). Combined: .card#main = div(class="card" id="main").
No — this tool converts HTML → Pug only. Compiling Pug → HTML requires the Node.js Pug compiler. Run it locally with npx pug --pretty file.pug.
"Jade" was trademarked by another software company, so the project was renamed to Pug in 2016. The syntax is identical.