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Code

6 Free Online Code Tools

These 6 tools handle the small code jobs that are not worth opening an editor for. HTML Beautifier and JS Beautifier / Minifier take markup or a script that arrived on one line and give it back with real indentation — or go the other way and strip it down before shipping. Regex Tester shows matches highlighted as you type, which turns a regular expression from guesswork into something you can watch working. Markdown Preview renders GitHub Flavored Markdown side by side with the source, so a README looks right before you push it. Code Playground goes furthest: a VS Code editor with HTML, CSS, and JavaScript panes, a live preview, and a console, for when you want to reproduce a bug in isolation rather than in your real project.

All 6 Code tools

What you can do with these code tools

The common thread is a fast round trip — paste, see the result, copy it back out.

  • Beautify — turn minified or badly indented HTML and JavaScript back into readable code with consistent indentation.
  • Minify — strip comments and whitespace from JavaScript to cut bytes before deployment.
  • Test regular expressions — write a pattern, run it against sample text, and see every match highlighted live with the flags you choose.
  • Preview Markdown — write on the left, see rendered HTML on the right, with GitHub Flavored Markdown tables and code fences.
  • Prototype — run HTML, CSS, and JavaScript together in a sandboxed playground with a console, no build step and no local setup.

Formatting locally versus pasting into a website

Most online beautifiers post your code to a server to format it. That is fine for a public snippet and a bad idea for anything from a private repository, which is why these run in the browser instead — the code never leaves the tab. It also means they keep working on a plane or behind a strict firewall. One caveat worth knowing: a beautifier reformats, it does not fix. If your JavaScript has a syntax error, beautifying it will not reveal the bug; run it in the Code Playground console instead, where you get a real error message and a line number.

Related categories

Frequently asked questions

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No. The beautifiers, the minifier, the regex tester, and the Markdown preview all run in your browser, so the code you paste never reaches a server. That makes them usable for work you cannot paste into a public website.

It uses the JavaScript regular expression engine built into your browser, with all the standard flags — global, case-insensitive, multiline, dotAll, sticky, and unicode. Patterns that rely on PCRE-only features such as lookbehind in older engines may behave differently elsewhere.

Yes, the JS tool does both directions. Minifying removes formatting and comments, so beautifying afterwards restores readable structure but not the original comments or line breaks — keep the source, not just the minified output.

It renders GitHub Flavored Markdown, including tables, task lists, fenced code blocks, and autolinks, so it is a close match for how a README will appear. GitHub-specific extras like issue references and emoji shortcodes are not resolved.

HTML, CSS, and JavaScript together, in a sandboxed frame with a live preview and a console for logs and errors. It is built on the Monaco editor, the same one that powers VS Code, so you get syntax highlighting and IntelliSense.

Yes, all 6 are free with no account and no usage limits, and they keep working offline once loaded.