Will minifying change how my code behaves?

Not on its own. Terser parses the code and only makes transformations it can prove are safe. The one thing that can break you is shortening names, and only when something looks a name up as text - eval, new Function, or dependency injection that reads parameter names. That switch is on the toolbar and you can turn it off.

Can it unminify a file back to the original?

It can make it readable, not original. Beautify puts back indentation and line breaks so you can follow the logic. Comments were deleted and short names stay short; nothing can recover "errorMessage" from "e". If you own the build, ship a source map - that is the only real answer.

What does the target setting change?

It tells Terser which syntax it is allowed to emit. On ES2020+ it may use arrow functions and other short modern forms; on ES5 it will not, so the output runs in older browsers. It does not translate your code - if you wrote an arrow function and pick ES5, it stays an arrow function. For that you need a compiler like Babel.

Is my code sent to a server?

No. Terser itself is downloaded to your browser and runs there, so the code never leaves your machine. That was the deciding factor in building the page this way: what people paste into a minifier is usually the source of something private, and a tool that needs to see it in order to shrink it is asking for too much.

JavaScript Minifier and Beautifier - Terser in Your Browser

Tools / / Dev Tools / Formatters / JavaScript Minifier

JavaScript minifier and beautifier

Target

Shorten names

Shortening local names saves the most bytes, but it breaks code that looks names up as text - inside eval, new Function, or a framework that reads parameter names. Turn it off if you rely on any of those.

Your JavaScript

var firstName = "Ada";
var lastName  = "Lovelace";
var fullName  = firstName + " " + lastName;

function greet(person, greeting) {
  // Minify deletes this comment; Beautify keeps it.
  const message = `${greeting}, ${person}!`;
  return message;
}

console.log(greet(fullName, "Hello"));

What this tool does

Minifying JavaScript is not stripping spaces. Doing it by search-and-replace produces files that look fine and behave differently, and the difference shows up in production. This page runs Terser - the same engine behind the build step of most projects - inside your browser.

How to use it

1 Paste the JavaScript into the box.
2 Choose a target and decide whether to shorten names.
3 Press Minify - or Beautify to open a minified file back up.

Why a parser and not search-and-replace

JavaScript inserts semicolons where you left them out. Remove the newline between "return" and its value and the function starts returning undefined - the file is still valid, it just does something else. The same character means division in one place and a regular expression in another. Telling these apart needs the grammar, not a pattern, which is why this page uses a real parser.

What actually gets smaller

Whitespace and comments are the smallest part of it. The real savings come from renaming local variables to single letters, merging separate declarations into one, folding constants, and dropping code that can never run. Those are all tree operations - the minifier has to know that two names refer to the same binding, and that nothing between them reads it.

Where shortening names bites

A minifier can rename what it can see. It cannot see a name written as text: eval("count + 1"), new Function("a", "return a"), or a framework that reads a function's parameter names to decide what to inject. Those keep looking for the old name and find nothing. This is a property of the language, not a flaw in the tool - which is why the switch is yours to make rather than something applied silently.

Beautify is not the original file back

Beautify restores indentation and line breaks, so a minified file becomes readable again. It cannot restore what was thrown away: comments are gone, and if names were shortened they stay short - no tool can guess that "e" was once "errorMessage". For debugging a production file, a source map is the only thing that brings the original back.

JavaScript minification - frequently asked questions

Terser - the successor to UglifyJS and the default minifier in webpack, Rollup and Vite. It is the same engine your build step already runs, which means the output here matches what you would get from a build, not an approximation of it.

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SQL Formatter Break a long query onto readable lines, or squeeze it back onto one. Keeps your keyword casing, your quoted names and your strings exactly as written.

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SQL Formatter Break a long query onto readable lines, or squeeze it back onto one. Keeps your keyword casing, your quoted names and your strings exactly as written.

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