Dev Tool

HTML Previewer

Write HTML, CSS, and JavaScript code and see a live preview instantly in a sandboxed iframe.

Code Editor1776 chars

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>My Page</title>
  <style>
    body {
      font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
      max-width: 800px;
      margin: 0 auto;
      padding: 40px 20px;
      background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
      color: #333;
      min-height: 100vh;
    }
    .card {
      background: white;
      border-radius: 16px;
      padding: 32px;
      box-shadow: 0 20px 60px rgba(0,0,0,0.15);
    }
    h1 {
      font-size: 2.5rem;
      margin: 0 0 16px 0;
      background: linear-gradient(135deg, #667eea, #764ba2);
      -webkit-background-clip: text;
      -webkit-text-fill-color: transparent;
    }
    p {
      font-size: 1.1rem;
      line-height: 1.7;
      color: #555;
    }
    .btn {
      display: inline-block;
      margin-top: 20px;
      padding: 12px 32px;
      background: linear-gradient(135deg, #667eea, #764ba2);
      color: white;
      border: none;
      border-radius: 8px;
      font-size: 1rem;
      cursor: pointer;
      transition: transform 0.2s, box-shadow 0.2s;
    }
    .btn:hover {
      transform: translateY(-2px);
      box-shadow: 0 8px 25px rgba(102, 126, 234, 0.4);
    }
  </style>
</head>
<body>
  <div class="card">
    <h1>Hello, World! 🚀</h1>
    <p>This is a live HTML preview. Edit the code on the left and click <strong>"Run"</strong> to see your changes instantly.</p>
    <p>Try changing the colors, text, or adding new elements!</p>
    <button class="btn" onclick="handleClick()">Click Me</button>
  </div>
  <script>
    function handleClick() {
      alert('Hello from the HTML Previewer! 🎉');
    }
  </script>
</body>
</html>

Live Preview

Introduction

Writing HTML without seeing the result is like painting in the dark. Whether you are crafting an email template, building a landing page prototype, or debugging a layout issue reported by a QA tester, you need to see how your markup renders before you commit it. An HTML previewer gives you a split-pane editor-and-preview workflow right in your browser — type or paste markup on the left, see the live render on the right, and iterate in real time without saving files or refreshing tabs.

What Is HTML Previewer?

HTML Previewer renders your HTML, CSS, and inline JavaScript in a live sandboxed iframe that updates as you type. It supports full document structures with head and body tags, embedded style blocks, and script elements — so you can test complete pages, not just fragments. The preview pane renders exactly as a browser would, including flexbox and grid layouts, CSS animations, and form element styling, giving you confidence that what you see is what your users will see.

The tool is designed for the rapid iteration loop that front-end development demands. You can prototype a responsive navigation bar, test whether a CSS grid template behaves correctly at different viewport widths, or verify that an email template renders in a table-based layout without switching between your editor and a browser. Error handling is built in — unclosed tags, invalid CSS properties, and JavaScript runtime errors are surfaced inline so you do not waste time wondering why a style is not applying.

The preview runs in a sandboxed iframe within your browser, so any scripts in your HTML execute in an isolated context. Your code never leaves your device, and there is no build step or server deployment required to see results. This makes it safe to test untrusted markup — such as user-generated content from a CMS — without risking your local environment.

HTML Previewer Examples

Input	Output
<div style="display:flex;gap:1rem"><div style="flex:1;background:#e0f2fe;padding:1rem">Column A</div><div style="flex:2;background:#fce7f3;padding:1rem">Column B</div></div>	Two-column flexbox layout rendered live: Column A takes 1/3 width with light blue background, Column B takes 2/3 with light pink background, 1rem gap between them
<style>@keyframes pulse { 0%,100% {opacity:1} 50% {opacity:0.3} }</style><div style="animation:pulse 2s infinite">Loading...</div>	Animated "Loading..." text that smoothly fades between full opacity and 30% opacity in a continuous 2-second loop
<table cellpadding="8" style="border-collapse:collapse"><tr><td style="border:1px solid #ccc">Cell 1</td><td style="border:1px solid #ccc">Cell 2</td></tr></table>	Single-row email-compatible table with two bordered cells, rendered without any external CSS framework dependency

Key Features of HTML Previewer

Live rendering in a sandboxed iframe that updates as you type with no manual refresh needed
Full document support including style blocks, script elements, meta tags, and link references
Responsive viewport toggle to preview layouts at desktop, tablet, and mobile widths
Inline error reporting for unclosed tags, invalid CSS, and JavaScript runtime errors
Auto-closing tag insertion and bracket matching in the code editor pane
Copy rendered HTML output or download it as a standalone .html file with one click
Dark mode preview to verify how your markup looks in browser dark-mode preferences

How It Works

Write HTML, CSS, and JavaScript in the Editor

Use the split-pane editor to type your markup, styles, and scripts. You can write everything in a single pane or separate your CSS and JS into their own sections. Paste existing code from your project or start a new experiment from scratch.

See the Live Preview Update Instantly

Every keystroke triggers an immediate refresh in the preview pane, showing exactly how your code renders in a real browser environment. CSS changes appear without a manual refresh, and JavaScript runs just as it would on a live page, including DOM manipulation and event listeners.

Copy or Export Your Working Code

When the preview looks right, copy the complete HTML document or individual CSS and JavaScript sections from the editor. The output is clean and unmodified from what you typed, so you can paste it directly into your project files without any additional cleanup.

Who Uses This

Web Development Students

learning HTML and CSS by typing code and immediately seeing how each element, property, and value affects the visual output without needing a local server setup

Frontend Developers

prototyping component layouts, testing CSS animations, or debugging layout issues in an isolated sandbox before moving code into their main project repository

Technical Bloggers

creating interactive code examples for tutorials by writing HTML, CSS, and JS in one place, then embedding the working preview alongside the source code in their articles

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Frequently Asked Questions

Can I use external JavaScript libraries?

You can include CDN links for libraries like React, Vue, jQuery, or D3 via a script tag in your HTML. The preview pane loads these just like a regular webpage would, so you can prototype with any library that has a public CDN.

Does the preview support responsive design testing?

The preview pane renders at whatever width your browser window provides. You can resize the window or use your browser's device emulation mode to test how your code looks at mobile and tablet breakpoints.

Will JavaScript errors crash the preview?

No. The preview catches runtime errors and displays them in a console-like output below the preview pane. Your code stays intact in the editor so you can fix the error and continue without losing any work.