liminfoHTML Live Preview
Free web tool: HTML Live Preview
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About HTML Live Preview
HTML Live Preview is a browser-based editor that renders your HTML, CSS, and JavaScript code in a sandboxed iframe in real time. The editor pane and the preview pane sit side by side in a responsive two-column layout. As you type, a 300-millisecond debounce timer waits for you to pause before re-rendering, ensuring the preview stays smooth without flickering on every keystroke. A manual Refresh button is also available for cases where you want to re-run scripts without changing the code.
Front-end developers, designers, educators, and students use this tool to prototype snippets, test CSS layouts, experiment with JavaScript interactions, and demonstrate HTML concepts without needing a local development environment. Because the preview runs inside a sandboxed iframe with the allow-scripts and allow-modals permissions, JavaScript runs normally — including alert(), event listeners, and DOM manipulation — but the frame cannot access the parent page, making it safe to run untrusted code.
Everything runs in your browser with no server involvement. The textarea accepts any valid HTML document including inline styles and script tags. The iframe is updated by writing code directly into the document via document.open(), document.write(), and document.close(). No data is uploaded; no account is needed. The tool works on desktop and tablet in the full split view, and falls back to a stacked single-column layout on narrow screens.
Key Features
- Split-pane layout: code editor on the left, live iframe preview on the right — 600px fixed height for comfortable editing
- 300ms debounced auto-refresh — the preview updates shortly after you stop typing, avoiding flicker on every keystroke
- Sandboxed iframe with allow-scripts and allow-modals — JavaScript including alert(), DOM events, and animations works fully
- Manual Refresh button to re-execute scripts and reload the preview without changing the source code
- Character count display updates in real time so you can track document size
- Accepts complete HTML documents with DOCTYPE, head, body, inline CSS, and inline JavaScript
- document.write() rendering for full page control — preview reflects exactly what the browser would render
- Fully client-side — no server upload, no rate limits, no account required
Frequently Asked Questions
What can I write in the HTML Live Preview editor?
You can write any valid HTML including complete documents with DOCTYPE declarations, meta tags, inline <style> blocks, inline <script> blocks, and body content. The iframe renders the entire document, so CSS and JavaScript both execute as they would in a real browser tab.
Does JavaScript run in the preview?
Yes. The preview iframe is sandboxed with allow-scripts and allow-modals permissions. Standard JavaScript including alert(), confirm(), addEventListener(), fetch(), setTimeout(), and DOM manipulation all work. The sandbox prevents the frame from accessing the parent page for security.
Why does the preview update with a short delay instead of instantly?
The 300-millisecond debounce prevents the iframe from re-rendering on every single keystroke, which would cause visible flickering and poor performance. The delay is short enough to feel real-time but long enough to batch consecutive keystrokes into a single render.
What does the Refresh button do?
The Refresh button manually triggers a re-render of the iframe without modifying the source code. This is useful when you want to restart JavaScript animations, re-execute scripts from scratch, or clear any runtime state that has accumulated in the preview.
Can I use external CSS frameworks or JavaScript libraries?
Yes. You can reference external resources via CDN links in your HTML. For example, add a Bootstrap CDN link tag in your <head> or a React CDN script tag before your code. The iframe will load those external resources as long as your network allows the requests.
Is this a replacement for CodePen or JSFiddle?
HTML Live Preview is a lightweight, privacy-focused alternative for quick prototyping without an account. CodePen and JSFiddle offer collaboration, saving, and sharing features, but require sign-up. This tool is best for fast, throwaway experiments where you just need to see what your code does without any setup.
Does the preview support responsive design testing?
The preview iframe is set to the full width of its container, so your HTML layout renders at the width of the preview pane. To simulate narrow viewports, you can resize your browser window to narrow the preview column. For precise responsive testing, use browser developer tools with device emulation.
Is the code I write stored anywhere?
No. The code lives only in the React state of the current browser session. It is not sent to any server, stored in localStorage, or persisted across page refreshes. When you close or refresh the browser tab, the code returns to the default example.