Run HTML, CSS & JS Online

Write complete web pages with HTML, CSS, and JavaScript — all in one editor.

Introduction

Modern web pages are built with three core technologies: HTML for structure, CSS for styling, and JavaScript for interactivity. Our online code runner supports all three in a single editor — write a complete web page and see it rendered instantly.

How to Write HTML, CSS, and JS Together

In our HTML Code Runner, you write a complete HTML document that includes CSS and JavaScript inline. Here's how they work together:

  • HTML — Define the structure and content of your page
  • CSS — Add styles using <style> tags in the <head>
  • JavaScript — Add interactivity using <script> tags

Example: Combined HTML, CSS, and JavaScript

<!DOCTYPE html>
<html>
<head>
  <style>
    body { font-family: sans-serif; text-align: center; padding: 2rem; }
    button { padding: 0.8rem 2rem; font-size: 1.1rem; cursor: pointer; }
    #counter { font-size: 3rem; margin: 1rem; color: #6C5CE7; }
  </style>
</head>
<body>
  <h1>Click Counter</h1>
  <div id="counter">0</div>
  <button onclick="count()">Click Me</button>
  <script>
    let n = 0;
    function count() {
      n++;
      document.getElementById('counter').textContent = n;
    }
  </script>
</body>
</html>

What You Can Build

  • Interactive forms with validation
  • Animated landing pages
  • Data visualization dashboards
  • Game prototypes
  • CSS art and animations
  • API-connected applications (fetch external data)

Tips for Multi-Language Code

  • Put CSS in the <head> to avoid FOUC (flash of unstyled content)
  • Put JavaScript at the end of <body> or use defer
  • Use the console output panel to debug JavaScript errors
  • Test responsive designs by resizing your browser window

Frequently Asked Questions

Yes. Use link tags for CSS and script tags with src attributes to load external resources from CDNs.

Yes. Include the Bootstrap CDN link in your HTML head section and all Bootstrap classes will work in the preview.

Yes. Include the jQuery CDN script tag and you can use jQuery syntax in your code.

Related Resources