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HTML/CSS/JS Sandbox

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Write HTML, CSS, and JavaScript in three tabbed editors and see a live preview instantly. Great for prototyping, teaching, or quick experiments.

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How to use HTML/CSS/JS Sandbox

  1. Write or paste HTML in the HTML tab, CSS in the CSS tab, and JS in the JS tab.
  2. Toggle Auto-run to see changes live as you type, or click Run to manually refresh the preview.
  3. Experiment and iterate — the iframe sandbox keeps your code isolated.
  4. Click Download HTML to save your work as a standalone file.

What is HTML/CSS/JS Sandbox?

This sandbox combines your HTML, CSS, and JS into a single document and renders it in a sandboxed iframe using a blob URL. The preview updates automatically (debounced 500ms) when the Auto-run toggle is on, or manually when you click Run. All execution is isolated in the iframe — no script in the sandbox can access the parent page.

Use the tabs to switch between editors. Download your work as a standalone HTML file. The default sample is a simple counter app you can modify or replace entirely.

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FAQ

Is this like CodePen or JSFiddle?
It's a lightweight client-side alternative. No accounts, no servers, no build step. Just write code and see the result instantly. For complex projects with multiple files, CodePen or StackBlitz are better options.
Can I use external libraries like React?
Yes — include CDN links in your HTML (e.g. <code>&lt;script src="https://unpkg.com/react/umd/react.development.js"&gt;</code>). The sandbox executes whatever you put in the HTML, CSS, and JS panels.
Is my code saved?
No. Everything runs in your browser. Use the Download HTML button to save your work locally. There is no server-side storage.

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