Code Playground: Write and Preview HTML, CSS, and JS Live

Why developers need a zero-setup code playground

You have an idea for a layout, a CSS animation, or a small JavaScript utility. You do not want to create a new project directory, run `npm init`, install dependencies, and set up a dev server just to test a ten-line snippet. You want to open a tool, write the code, and see it work immediately. That is exactly what this playground does: a text editor on the left, a live preview on the right, and zero friction between typing and seeing the result.

The playground supports HTML, CSS, and JavaScript in a single editing environment. Write your markup in the HTML section, style it in the CSS section, and add interactivity in the JavaScript section — or put everything in a single HTML block with inline `<style>` and `<script>` tags. The preview renders in a sandboxed iframe, which means your code runs in a real browser context with access to the DOM, `fetch`, `localStorage`, and all standard Web APIs. You can even load external libraries by adding CDN `<script>` tags in the HTML head.

Everything runs locally in your browser. No code is sent to any server, no account is required, and once the page loads the playground works without an internet connection. You can download your work as an HTML file at any time.

Playground capabilities and features

How to use the code playground

Write or paste your HTML, CSS, and JavaScript code in the editor panel on the left

Click Run or wait for the live preview to update automatically as you type

See the rendered result in the preview panel on the right — the iframe runs a complete browser context

Download your code as an HTML file using the download button, or copy the code directly from the editor

Testing with a real project example

Build a simple interactive component: create a button in HTML, style it with CSS transitions (background color change, scale transform on hover), and add a click handler in JavaScript that increments a counter displayed on the page. The live preview should show the styled button immediately and update the counter on each click. This tests all three languages working together and confirms that event listeners, DOM manipulation, and CSS all render correctly in the sandboxed iframe.

Test with an external library: add a Tailwind CSS CDN link in the HTML head and use Tailwind utility classes in your markup. The preview should render the Tailwind-styled layout correctly. Then add a fetch call to a public API (like JSONPlaceholder) and display the results in a list. This confirms that network requests work within the iframe sandbox. If the external library does not load, check that the CDN URL is correct and that you are not in an offline environment.

Common playground mistakes

Forgetting that JavaScript runs in a sandboxed iframe — it cannot access the parent page's DOM, cookies, or localStorage

Using ES modules (`import`/`export`) without a module bundler — the iframe executes scripts as classic scripts unless you use a CDN that supports modules

Expecting server-side features — the playground is client-side only, so no Node.js APIs, no `fs`, no `require`, and no server-side rendering

Not saving your work — there is no cloud save, so download your code as an HTML file before closing the tab

Understanding the iframe sandbox and its implications

The preview renders inside a sandboxed iframe, which provides isolation between your playground code and the tool itself. This means your JavaScript can access standard browser APIs (DOM, `fetch`, `localStorage`, `requestAnimationFrame`, `Web Workers`) but cannot access the parent page's variables, cookies, or storage. This is a security feature, not a limitation — it ensures that code running in the preview cannot interfere with the playground's own functionality.

The sandbox also means that some advanced features behave differently than they would in a full development environment. Service workers, for example, require a registered scope that the iframe cannot provide. WebRTC connections work but may prompt for camera/microphone permissions in ways that differ from a standalone page. For production development, use the playground for prototyping and then move your code into a proper project with a dev server and build tool.

Who uses a code playground

Frontend developers prototyping UI components, CSS animations, or layout ideas without setting up a new project

Technical interviewers and candidates running live coding exercises in a shared browser tab

Educators and students following along with web development tutorials in an interactive environment

Designers converting Figma concepts to code by writing HTML/CSS and seeing the result immediately

Developers debugging a small code snippet from Stack Overflow or documentation before integrating it into their project

Frequently asked questions

Q: Does this tool support external libraries?

A: Yes — you can add CDN links in the HTML head. For example, add a Tailwind CSS or Alpine.js CDN script tag and use the library in your code immediately.

Q: Is my code uploaded anywhere?

A: No. All code runs in your browser via an iframe. Nothing is sent to any server.

Q: Can I save my work?

A: You can download the code as an HTML file. There's no cloud save feature — everything stays local.

Q: Does it support ES6+ JavaScript?

A: Yes. The preview iframe uses your browser's JavaScript engine, which supports all modern JavaScript features.

Q: Can I use this tool offline?

A: Yes. Once the page loads, the playground works without an internet connection.

Start coding now

Write and preview HTML, CSS, and JavaScript with the Code Playground. Optimize your CSS output with the CSS Minifier & Beautifier. Compress JavaScript with the JS Minifier & Beautifier. Convert HTML to Markdown with the HTML to Markdown Converter or format source code with the Code Formatter.