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What Is HTML Live Preview?
HTML Live Preview is an in-browser code editor that renders your HTML, CSS, and JavaScript in real time. As you type, the output panel updates instantly, giving you immediate visual feedback without switching between an editor and a browser tab.
The preview runs inside a sandboxed iframe with strict security restrictions. This means your code executes in an isolated environment — it cannot access the parent page, cookies, or local storage. You get a safe playground for experimentation without any risk to the host application.
How Live Preview Works
The editor combines your HTML, CSS, and JavaScript into a single document and injects it into a sandboxed iframe. Updates are debounced to keep the preview responsive without overwhelming the browser.
- Sandboxed iframe — the preview runs with sandbox="allow-scripts" only, blocking access to the parent page, cookies, forms, and navigation for full isolation
- Separate code tabs — write HTML, CSS, and JavaScript in dedicated panels, each with syntax-appropriate editing, combined automatically on render
- Debounced updates — changes are applied after a short pause in typing, keeping the preview smooth and avoiding constant re-renders on every keystroke
Try it free — no signup required
Try HTML Live Preview →When To Use HTML Live Preview
Live preview is ideal whenever you need quick visual feedback on HTML and CSS without a full development environment.
- Rapid prototyping — test layout ideas, color schemes, and component designs instantly without setting up a build tool or dev server
- Learning HTML and CSS — beginners can see the effect of every tag and property immediately, making the learning loop much tighter
- Email template testing — preview HTML email layouts with inline styles to check rendering before sending, since email clients have limited CSS support
Frequently Asked Questions
Is the preview secure? Can my code access the parent page?
The preview is fully sandboxed. The iframe uses sandbox="allow-scripts" without allow-same-origin, which means your code can run JavaScript but cannot access the parent page's DOM, cookies, localStorage, or session data. This is the same security model used by platforms like CodePen and JSFiddle.
Why is allow-same-origin not included in the sandbox?
Including allow-same-origin with allow-scripts would let the previewed code escape the sandbox entirely — it could access the parent page's cookies, modify the DOM, or read sensitive data. Omitting it ensures complete isolation. The trade-off is that localStorage and sessionStorage are unavailable inside the preview, but this is a deliberate security choice.
Can I load external CSS or JavaScript libraries in the preview?
Yes. You can add link and script tags referencing CDN URLs (e.g., Bootstrap, Tailwind, jQuery) in your HTML panel. The sandboxed iframe allows network requests to load external resources. Just keep in mind that external scripts also run under the sandbox restrictions — they cannot access the parent page either.