HTML Preview

The tool splits into two areas: an editor where you write HTML (with optional <style> and <script> blocks, or separate CSS/JS panes) and a live preview that re-renders whenever your code changes. There's no compile or save cycle; the preview reflects the current state of your editor.

Under the hood, your markup is injected into a sandboxed preview frame and rendered by the browser's own engine. That means the output is exactly what a real browser produces, not an approximation. CSS layout, flexbox, grid, media queries, and modern JavaScript all behave the way they would on a normal page.

Key things it gives you:

• Live render as you type, including styles and scripts
• Real browser output, so what you see matches a deployed page
• Isolation, so a runaway script or broken layout can't affect the editor itself
• Zero setup, so there's nothing to install or configure

Say you want to check how a button looks with a hover transition. Paste this into the editor:

<style>
  .cta {
    padding: 10px 18px;
    border: none;
    border-radius: 6px;
    background: #2563eb;
    color: white;
    cursor: pointer;
    transition: background 0.2s;
  }
  .cta:hover { background: #1e40af; }
</style>

<button class="cta" onclick="this.textContent='Clicked'">
  Click me
</button>

The preview shows the styled button right away. Hover it and the background animates; click it and the JavaScript updates the label. You can tweak the colors, padding, or transition timing and watch each change land without reloading anything. This is the core loop: edit a value, see the effect, repeat. It's much faster than editing a file, saving, and alt-tabbing to a browser to refresh.

The tool fits a handful of recurring needs:

• Testing a snippet someone shared in a chat, an answer, or documentation, without trusting it inside your real project
• Prototyping a component (a card, a form, a nav bar) in isolation before wiring it into a larger codebase
• Debugging a layout by stripping a problem down to the minimum HTML and CSS that reproduces it
• Learning by experimenting with a CSS property or a DOM API and seeing the result instantly
• Quick demos where you want to show a colleague a working example rather than describing it

Because it runs locally and needs no account, it's also handy when you're on a locked-down machine, an offline-ish network, or simply don't want to create yet another login to test ten lines of code.

A few things that trip people up:

• External resources need full URLs. A relative path like images/logo.png has nothing to resolve against here, so reference assets with absolute https:// URLs or inline them as data URIs.
• Scripts run in a sandbox. APIs that require a trusted origin, permissions, or a real domain (for example, certain storage, clipboard, or camera features) may be restricted by the preview frame's sandbox.
• fetch is subject to CORS. Requests to other origins still need the server to send the right CORS headers, exactly as they would on any web page.
• Order matters. A <script> that touches an element must run after that element exists in the DOM, or wrap it in a DOMContentLoaded handler.
• The preview is ephemeral. If you want to keep what you wrote, copy it out, because it lives in the current session, not a saved file.

Live HTML preview means running code you may not fully trust, including snippets pasted from the internet. To keep that safe, the preview renders inside a sandboxed frame: an isolated browsing context that the browser deliberately restricts.

Sandboxing limits what the previewed code can reach. It can't read or modify the editor around it, and depending on the sandbox flags in effect, capabilities like top-level navigation, popups, or certain origin-bound APIs are blocked. This is the same mechanism real applications use to embed untrusted content safely.

The practical upside for you: a broken or malicious snippet stays contained. An infinite loop or a script that tries to redirect the page can't take over the tool or your tab. The tradeoff is that some browser features genuinely require a real, trusted origin and won't work inside a sandbox. That's a security boundary doing its job, not a bug. For most editing, prototyping, and debugging, the sandbox is invisible and everything renders normally.