HTML Previewer

HTML Previewer - Online HTML CSS JavaScript Sandbox Editor

A professional HTML previewer and sandbox environment for testing HTML, CSS, and JavaScript code in real-time. Features split-screen editor, live preview, console output, fullscreen mode, templates, and more. Perfect for learning web development, prototyping, testing code snippets, and sharing examples.

What is an HTML Previewer/Sandbox?

An HTML Previewer (also called sandbox or playground) is an interactive environment where you can write and test HTML, CSS, and JavaScript code with instant visual feedback. It's useful for:

- Learning web development
- Testing code snippets
- Prototyping designs
- Debugging HTML/CSS issues
- Sharing code examples
- Experimenting with new features
- Quick demos and proofs of concept

Similar to CodePen, JSFiddle, and other online code editors, but simpler and runs entirely in your browser.

How do I use this HTML Previewer?

Using the previewer is simple:

1. Choose a tab: HTML, CSS, or JavaScript
2. Write your code in the editor
3. Click 'Run Code' or enable 'Auto-run' for instant preview
4. View the result in the Preview pane
5. Check the Console tab for JavaScript logs and errors
6. Use templates to get started quickly
7. Toggle fullscreen for larger workspace

Tips:
- Enable Auto-run for real-time updates as you type
- Use templates to learn common patterns
- Check Console for JavaScript errors
- Download your code when done

What are the editor features?

The editor includes professional features:

Code Editing:
- Syntax highlighting for HTML, CSS, JavaScript
- Line numbers for easy reference
- Auto-indentation
- Tab support (press Tab to indent)
- Word wrap option
- Adjustable font size

Preview Features:
- Live preview in isolated iframe
- Auto-run or manual execution
- Console output for debugging
- Fullscreen preview mode
- Responsive preview

Layout Options:
- Horizontal split (editor left, preview right)
- Vertical split (editor top, preview bottom)
- Adjustable split sizes

Other Features:
- Pre-built templates
- Download as HTML file
- Clear all code
- Copy to clipboard

Can I use external libraries?

Yes! You can use external libraries by including them in your HTML:

CSS Libraries:
<link href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css" rel="stylesheet">

JavaScript Libraries:
<script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/js/bootstrap.bundle.min.js"></script>

Common CDNs:
- jsDelivr: cdn.jsdelivr.net
- cdnjs: cdnjs.cloudflare.com
- unpkg: unpkg.com

You can include:
- CSS frameworks (Bootstrap, Tailwind, Bulma)
- JavaScript libraries (jQuery, Vue, React)
- Icon libraries (Font Awesome)
- Any public CDN resource

What's the difference between Auto-run and Manual run?

Two execution modes are available:

Auto-run (Real-time):
- Code runs automatically as you type
- Instant preview updates
- Great for quick experiments
- Updates with small delay (debounced)
- May slow down with complex code
- Best for HTML/CSS work

Manual Run:
- Code runs only when you click 'Run Code'
- More control over execution
- Better performance for complex code
- Prevents accidental infinite loops
- Best for JavaScript development
- Recommended for learning

You can toggle between modes anytime using the Auto-run checkbox.

How does the Console work?

The Console tab captures JavaScript output:

What it shows:
- console.log() output
- console.error() messages
- console.warn() warnings
- console.info() information
- Runtime errors and exceptions

Features:
- Color-coded message types (log, error, warn)
- Timestamps for each message
- Clear console button
- Preserves history during session
- Shows error line numbers

Examples:
console.log('Hello World');
console.error('This is an error');
console.warn('Warning message');

The console helps you debug JavaScript code and see what your code is doing.

Can I save or share my code?

You can save and share your work:

Save Options:
- Download as complete HTML file (includes CSS and JS)
- Copy code to clipboard
- Save manually in your browser (Ctrl+S works in editors)
- Use browser localStorage (code persists on refresh)

Sharing:
- Copy code and share via email, chat, etc.
- Download and attach to messages
- Include in documentation
- Paste into other tools

Note: This tool doesn't provide cloud storage or URLs for sharing. For permanent hosted sharing, use platforms like CodePen, JSFiddle, or GitHub Gists.

What are Templates?

Templates are pre-built code examples to help you get started:

Available Templates:
- Blank: Empty editor to start from scratch
- Basic HTML: Simple HTML5 structure
- Bootstrap Starter: Bootstrap 5 framework setup
- Flexbox Layout: CSS Flexbox example
- CSS Grid: Modern grid layout example
- CSS Animation: Interactive animation demo

Templates are great for:
- Learning new concepts
- Starting projects quickly
- Understanding code patterns
- Testing frameworks
- Getting inspiration

You can load a template and modify it to suit your needs.

Is my code safe and private?

Yes, your code is completely safe and private:

- All code runs entirely in your browser
- No code is sent to any server
- We don't store, log, or track your code
- No cloud storage or databases
- No analytics on code content
- Works offline after page load

Security features:
- Preview runs in sandboxed iframe
- Limited access to parent page
- No access to your file system
- JavaScript runs in isolated context

Best practices:
- Don't include real API keys or passwords
- Test with sample data
- Be cautious with user input
- Validate and sanitize data

The tool is designed for safe experimentation and learning.

What are the keyboard shortcuts?

Useful keyboard shortcuts:

Editing:
- Tab: Indent code
- Shift+Tab: Outdent code
- Ctrl/Cmd+A: Select all
- Ctrl/Cmd+C: Copy
- Ctrl/Cmd+V: Paste
- Ctrl/Cmd+Z: Undo
- Ctrl/Cmd+Y: Redo

Execution:
- Ctrl/Cmd+Enter: Run code (when in editor)
- Ctrl/Cmd+L: Clear console

Navigation:
- Ctrl/Cmd+1: Focus HTML editor
- Ctrl/Cmd+2: Focus CSS editor
- Ctrl/Cmd+3: Focus JavaScript editor
- F11: Toggle fullscreen (browser)

Note: Some shortcuts may vary by browser and operating system.

Key Features

• Write HTML, CSS, and JavaScript in tabbed editors
• Live preview with instant updates
• Auto-run mode for real-time preview
• Manual run mode for controlled execution
• Split-screen layout (horizontal or vertical)
• Fullscreen preview mode
• Console output for JavaScript debugging
• Syntax highlighting for all languages
• Line numbers and code formatting
• Multiple pre-built templates
• Download as complete HTML file
• Copy code to clipboard
• Adjustable font size
• Word wrap option
• Error detection and display
• Sandboxed iframe for safe execution
• Support external libraries via CDN
• Dark mode support
• 100% client-side - no server required
• Works offline after initial load
• Responsive design for all devices
• No registration or login needed