Run HTML, CSS and JavaScript in Your Browser
Free browser-based tool to write, run, and preview HTML, CSS, and JavaScript instantly — no download, no account, no install. Live preview powered entirely by your browser.
Instant Live Preview
Auto-run re-renders 700 ms after you stop typing.
Three-Tab IDE
Separate HTML, CSS, and JS panels like a real IDE.
Fully Responsive
Works on desktop, tablet, and mobile screens.
Sandboxed & Safe
Runs 100% locally in your browser. Nothing sent to any server.
Light & Dark Theme
Toggle between dark and light editor themes.
Full HTML5 + ES2023+
Canvas, Web Audio, Fetch, localStorage — all supported.
What Does This HTML Runner Do?
The HCODX runner combines your HTML, CSS and JavaScript into a preview document and opens it in an isolated browser frame. The browser parses HTML, applies CSS and runs JavaScript. This is useful for testing a small front-end example; it is not a server-side compiler for HTML.
Unlike desktop IDEs, an online HTML runner requires zero setup and works on any device: Windows, macOS, Linux, Android, or iOS. The HCODX HTML Runner is part of a full browser-based IDE platform.
How to Run an HTML Example Online
Open the tool
Visit this page in any modern browser — no login or install required.
Write HTML
Type or paste markup into the index.html tab.
Add CSS & JS
Switch to styles.css for styles and scripts.js for logic.
Run
Press Run or Ctrl+Enter. Enable Auto-run for live preview as you type.
Export
Use the open-in-new-window button to pop the result in its own tab.
Keyboard Shortcuts
About HTML — The Language of the Web
HTML (HyperText Markup Language) is the foundational language of the World Wide Web, first proposed by Tim Berners-Lee in 1991. Every webpage uses HTML to define semantic structure — headings, paragraphs, links, images, tables, and forms — which CSS then styles and JavaScript makes interactive.
The HCODX HTML Viewer supports the full HTML5 spec, all modern CSS3 features (Grid, Flexbox, animations, custom properties, container queries), and the complete ECMAScript 2023+ API. External CDN libraries, <canvas>, Web Audio, SVG, Fetch, and localStorage all work exactly as in a real browser.