Write HTML, CSS, and JavaScript with real-time live preview rendering in an isolated sandbox iframe.
HTML Live Preview turns a browser-ready snippet into a running document beside the source. Paste HTML, with CSS in style elements or attributes and JavaScript in script elements, and the preview reflects the rendered result as you edit. It is intended for checking DOM output, visual styling, and small client-side behaviors without creating a project. The important context is the preview boundary: the result is inside an isolated sandbox iframe rather than a normal top-level page, so navigation, origin-sensitive features, permissions, and access to the surrounding tool page may not match deployment.
A concrete input and expected output from the current implementation.
Input
<!doctype html>
<html>
<body>
<p id="answer"></p>
<script>
document.getElementById("answer").textContent = String(6 * 7);
</script>
</body>
</html> Expected output
42
The paragraph is parsed before the script runs. 6 times 7 is 42; String converts that number to text, and textContent makes 42 the paragraph's visible content.
HTML Live Preview interprets the entry as document source, so browser parsing rules apply. HTML creates elements, CSS rules style those elements, and an ordinary inline classic script such as the one in the example runs when parsing reaches it. In the example, the target paragraph appears before the script that selects it. If that order were reversed without waiting for later parsing, the selector would not find the paragraph at that moment.
The rendered result has its own document and browsing context inside the sandbox iframe. DOM calls such as document.querySelector() operate on the preview document, not on HTML Live Preview's editor controls. The sandbox also places boundaries around actions that normally involve a parent or top-level page. Exact behavior for such actions depends on the permissions granted to that iframe.
Yes. Browser-ready JavaScript in script elements can read and modify the preview DOM, attach event listeners, and calculate displayed values, as the example does. No, a correct result here does not prove identical production behavior. Script ordering, the iframe sandbox, origin rules, external dependencies, and the eventual host page can all affect the same code.
No, not when that source requires compilation or server-side processing. HTML Live Preview is for code a browser can execute as HTML, CSS, and JavaScript. PHP and server templates must be rendered elsewhere first. JSX or TypeScript must be transformed to browser-ready JavaScript. Paste the generated output, or use the project toolchain that normally builds it.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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