Frequently Asked Questions
Answers about running HTML, CSS, and JavaScript online, sandboxing, downloads, and mobile use.
What is an HTML CSS JS compiler?
It is an online workspace that combines HTML, CSS, and JavaScript into a live browser preview so you can write and test frontend code quickly.
Can I run HTML, CSS, and JavaScript together?
Yes. The preview document injects your CSS into a style tag and your JavaScript into a script tag around your HTML.
Is the compiler free?
The core playground is available in the browser without creating an account for basic use.
Do I need to install anything?
No. Open the site and start editing. A modern browser is enough.
Does the compiler work on mobile?
Yes. Editors, Run, preview, and console are arranged for smaller screens with tabbed panes.
Does my code run in the browser?
Yes. Preview rendering and script execution happen locally in a sandboxed iframe.
Can I download my code?
Yes. Download builds a standalone index.html that includes your HTML, CSS, and JavaScript.
Can I test JavaScript?
Yes. Use the JavaScript pane, then inspect console messages and runtime errors after Run.
Can I test responsive designs?
Yes. Switch between desktop, tablet, and mobile preview widths and read the viewport label.
Does the compiler save my code?
When local saving is enabled by normal editing, your panes may be stored in this browser via localStorage.
Is my code uploaded to a server?
Standard preview does not require uploading editor contents to a backend. Your browser performs the render.
Why isn't my JavaScript working?
Common causes include running before the DOM node exists, typos in IDs, blocked permissions in the sandbox, or relying on APIs unavailable in iframe contexts. Check the console panel for details.
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A fast browser-based HTML, CSS and JavaScript development playground.