How does JavaScript minification work?

Minification removes unnecessary characters from JavaScript without changing what the code does. This tool uses Terser, the same engine used by Webpack and Rollup, to mangle variable names (renaming userName to n, for example), perform dead-code elimination and constant folding, and strip comments and whitespace. Everything runs in your browser; nothing is uploaded to any server.

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JavaScript Minifier.

Paste code, upload a .js file, or fetch a URL. Variables get mangled, comments stripped, whitespace squeezed. Minification runs in your browser using Terser, the same engine Webpack and Rollup use.

// upload .js file // or fetch from URL

// source JavaScript

// mangle variable names // compress (dead code, constant folding)

// minified output

// minification powered by Terser v5.36.0 · BSD-2-Clause license · original work by Fábio Santos and contributors

// how it works & attribution

Minification is handled by Terser, the JavaScript mangler/compressor used by Webpack, Rollup, Parcel, and most modern bundlers. The library is loaded once from a public CDN (cdn.jsdelivr.net/npm/terser@5.36.0), then your code is minified entirely in this browser tab. Nothing is sent to any server.

Mangle renames local variables to single letters (userName → n). Big wins, but breaks any code that relies on names existing at runtime (some legacy DI containers, certain angular.js patterns). Turn it off if you hit issues.

Compress performs dead-code elimination, constant folding, boolean simplification, and other AST rewrites. Safe for nearly all code; rare issues come up with code that depends on Function.prototype.toString() or live-edited source.

URL fetch limitations: browsers block cross-origin requests by default. The "Fetch" button only works for URLs served with permissive CORS headers (most public CDNs, including jsdelivr, unpkg, and cdnjs, allow this; most private hosts don't). If a fetch fails, paste the code instead or download the file and use Upload.

Privacy: your code never leaves your browser. Verify in the Network tab: you'll see the Terser library download once on first use, and nothing else.

Attribution: this tool is a thin wrapper around Terser (BSD-2-Clause). Terser is a fork of UglifyJS3, originally by Mihai Bazon. All minification credit belongs to the Terser maintainers.

Related: need to minify stylesheets? The CSS Minifier does the same browser-local treatment for CSS. Working with JSON instead of JavaScript? The JSON Formatter & Validator handles JSON payloads.

// a free, browser-only tool by Tiempo Software, built in Omaha, Nebraska. Runs entirely in your browser; nothing you enter is uploaded. see all tools.