Frequently Asked Questions

HTML Code Runner is a free, browser-based tool that lets you write, run, and preview HTML code instantly. It supports HTML, CSS (via <style> tags), and JavaScript (via <script> tags). Your code runs in a sandboxed iframe without any server-side processing, meaning nothing is stored or transmitted.

When you click Run, the HTML code from the editor is wrapped into a Blob object, converted to a Blob URL, and loaded into a sandboxed <iframe>. This isolates the preview from the main page while allowing scripts to execute. The console output from the iframe is captured and displayed in the Console Output panel.

Yes. HTML Code Runner is 100% free with no hidden costs, subscriptions, premium tiers, or paywalls. You can use it as often as you like.

Yes. You can write a complete HTML document including <style> blocks for CSS and <script> blocks for JavaScript. The runner renders the full document, so styles, layouts, and interactive scripts all work as expected.

No. Your code runs entirely in your browser and is never sent to any server. Nothing is stored, logged, or tracked. If you want to save your work, use the Download button to save a local .html file.

Yes. The code runs inside a sandboxed iframe that is isolated from the rest of the page and your browser. It cannot access your cookies, local storage, or other browser tabs. That said, only run code you trust — especially if it includes JavaScript from unknown sources.

Yes. The interface is fully responsive. On smaller screens, the editor and preview panels stack vertically. While a desktop keyboard offers a better coding experience, the tool is functional on phones and tablets for quick edits.

No. There is no signup, login, or registration required. Just visit the homepage and start coding immediately.

Yes. Click the Download button in the editor toolbar to save your code as a .html file. You can then open it in any browser or text editor.

All modern browsers are supported: Chrome, Firefox, Safari, Edge, Opera, and Brave. The tool requires JavaScript to be enabled. Older browsers like Internet Explorer may not work correctly.

Absolutely. Teachers and instructors can use it to demonstrate HTML concepts in real time. Students can follow along on the same page on their own devices and experiment with the code.

HTML Code Runner is designed for simplicity and privacy. There is no account, no code storage, and no sharing features. It is a single-file, zero-friction HTML testing tool. If you need project management, collaboration, or code sharing, platforms like CodePen may be more suitable.

Yes. You can include CDN-hosted libraries, Google Fonts, images, and any external resources using standard HTML tags (<link>, <script>, <img>). Resources must be publicly accessible and support cross-origin requests.

JavaScript errors are captured and displayed in the Console Output panel below the editor. HTML and CSS errors are handled by the browser naturally — they will render as the browser interprets them, just like in a normal web page.

There is no artificial character limit. However, extremely large documents may cause performance issues depending on your device's capabilities and your browser's memory.