Live Code Compiler

What is a Live Code Compiler?

A live code compiler (also called a playground or sandbox) is a browser-based editor that lets you write HTML, CSS, and JavaScript and immediately see the rendered result in a preview pane. There's no setup, no build step, and nothing to install - everything runs locally in your browser using a sandboxed iframe.

What you can do with this tool

• Write HTML - just the content you want to render, no boilerplate needed.
• Style with CSS - add any valid CSS targeting the HTML you wrote.
• Add JavaScript - vanilla JS that runs against the rendered DOM.
• Live preview - click Run to execute and see the result.

Who it is for

A playground is the quickest way to answer a small front-end question without creating files or starting a server. Students use it to practise the basics of web pages, developers use it to test a CSS layout or reproduce a bug in a few lines, and teachers use it to show how a change in one language affects the result. Note that nothing is compiled in the traditional sense: HTML, CSS and JavaScript are interpreted directly by your browser, which is exactly what makes the result instant.

How to use it

1. Type or paste markup into the HTML box. You only need the content of the page, such as headings, paragraphs and buttons.
2. Add styles to the CSS box. Write normal rules like h1 { color: teal; }, without a <style> tag.
3. Add code to the JavaScript box, again without a <script> tag.
4. Click Run. The preview is rebuilt from scratch, so state from the previous run is gone. Click Clear to empty all three boxes and the preview.

How the preview is assembled

When you click Run, the tool builds one small document. Your CSS goes inside a <style> element in the head, your HTML becomes the body, and your JavaScript goes in a <script> element placed after the HTML. Because the script runs last, every element you wrote already exists, so document.querySelector('h1') works without waiting for a load event.

A quick example: put <button id="b">Count</button> <p id="n">0</p> in HTML and let c = 0; b.onclick = () => n.textContent = ++c; in JavaScript. Run it and every click increases the number.

Limits of the sandbox

• No pop-ups or dialogs - alert(), confirm() and new windows are blocked by the sandbox. Write messages into the page or use the browser console instead.
• No form submission - forms cannot be posted. Handle the submit event in JavaScript and call preventDefault().
• No storage - the preview has no origin of its own, so localStorage and cookies are not available.
• Classic script only - the JavaScript box is not an ES module, so import statements fail there. Add a <script type="module"> tag inside the HTML box if you need modules.
• No auto-save - your code lives only in this tab. Copy it somewhere safe before you close or reload the page.

Privacy & safety

Your code never leaves your browser. The preview runs inside a sandboxed iframe, so any JavaScript you execute is isolated from the rest of the page and cannot read this site's cookies or storage. The only network requests made are the ones your own code asks for, such as a library you load from a CDN.