HTML, CSS, and JavaScript Sandbox
Write HTML, CSS, and JavaScript side by side and watch a live preview render inside a sandboxed frame. It is a scratchpad for front-end experiments that needs zero setup.
How to use the HTML Preview Sandbox
- Enter markup in the HTML panel, styles in the CSS panel, and script in the JS panel.
- The preview refreshes as you edit each panel.
- Iterate until the layout or interaction behaves the way you want.
- Copy the pieces out when the experiment becomes real code.
When the HTML Preview Sandbox is useful
- Prototyping a layout or component before committing it to your project.
- Testing a CSS trick or JavaScript snippet in isolation.
- Reproducing a front-end bug with the smallest possible test case.
- Teaching web basics with immediate visual feedback for students.
How the HTML Preview Sandbox works
The preview runs inside an iframe sandbox, so the code you write executes with restricted privileges and cannot reach the parent page or your data. CSS applies to the sandbox document, and JavaScript runs with console output surfaced back to the page. Since the entire environment is your browser, experiments with unreleased designs or internal components stay on your machine.
Limits to keep in mind
Sandbox restrictions block network requests from the preview, and code that depends on external APIs may not behave exactly as it would on a real server.
Frequently asked questions
Can I use external JavaScript libraries?
The sandbox focuses on self-contained snippets; external scripts requiring network access are restricted.
Is my experiment saved anywhere?
No. The sandbox is ephemeral; copy anything you want to keep before closing the tab.
Why is my fetch call failing?
Sandboxed previews block network requests, so API calls cannot complete inside the tool.
Last reviewed: October 2026.