Why parser-based minification matters
Removing whitespace with simple find-and-replace rules can break code: a regular expression cannot tell a comment marker inside a string from a real comment, and stripping a newline can change how JavaScript inserts semicolons. Parser-based minifiers build a full syntax tree first, so they understand strings, regular expressions, template literals and scope, and only apply transformations that keep the meaning identical.
This page uses three widely used open-source tools that run entirely in the browser: Terser for JavaScript, CSSO for CSS and html-minifier-terser for HTML. They are bundled locally and loaded only when you open this tool.
Supported syntax and limitations
JavaScript must be valid ES2020 or later; TypeScript, JSX and non-standard syntax are not supported. Top-level names are preserved so global functions keep working. CSS must be standard CSS; preprocessor syntax such as Sass nesting with variables is not supported. HTML minification keeps attribute quotes where needed and does not remove optional tags, which keeps the output safe for most templates, but templating syntax such as Handlebars may need testing. Always keep your original source and test minified output before deploying.