How the sandbox runs your code

Your source is written into a sandboxed iframe and evaluated by the same engine that runs the rest of the page. There is no build step and no container to wait for, so the feedback loop is a keystroke rather than a deploy. Console output is captured and shown alongside the preview so you can log intermediate values.

Practical limits worth knowing

Because execution is local, an infinite loop will block the tab rather than time out on a server, and reloading clears it. Code that depends on a specific Node API, a bundler transform, or a cross-origin request that the target host does not allow will not behave the same here as in your app. For anything relying on your own backend, test against a local dev server instead.

Related utilities

For formatting and validating snippets rather than running them, see the developer tools, or browse the full catalog.