For developers, teachers and anyone testing an idea on a laptop or an iPad. There is no account and nothing to install. Once it has loaded it keeps working with the Wi-Fi off, and your code stays in your browser.
02 / WHAT IT DOES
Everything below happens in one browser tab.
Your code stays there until you share it or download it.
The preview sits next to your code and refreshes in about half a second. JSX compiles right in the browser, so there is no npm install and no build server to wait for.
After the first load it still works with the Wi-Fi off.
The editor completes syntax as you type. When code breaks, the common errors explain what went wrong in plain words.
There is no AI in CodeRunner, and that is a choice.
Pick a file, a folder or a whole React project and copy it as a link. The code travels inside the link, so nobody stores it for you.
Whoever opens it gets a temporary copy of their own and can save it to their files. Your version stays untouched. Projects too big for a URL get a clear message to download them instead.
Split code across files and folders and import between them with ES modules. Open files sit in editor tabs.
You can rename, move, upload and download files, and the Examples folder shows a multi-file project with imports already wired up.
Download Project gives you a ZIP of a Vite and React app with the usual src layout. Unzip it, run npm install and npm run dev, and you are in a normal project on your own machine.
The starter template is dark, and what you saw in the preview is what you get in the export.
unzip my-react-app.zipnpm installnpm run dev
03 / WHAT IT DOES NOT DO, ON PURPOSE
04 / START
Go to coderunner.lab829.com. No sign-up. Install it as an app if you want it offline. On an iPad, add it from Safari's share menu.
Open an example or create a React project, then write. The preview updates beside the editor.
Copy a share link for someone else, or download the project as a Vite and React app and keep going on your machine.
05 / QUESTIONS
In your browser, on your device. Nothing is uploaded. If you clear the browser's data for the site, the code goes with it, so download anything you want to keep.
Yes, after the first load. The editor, the runner and the React preview keep working with the Wi-Fi off. Installing it as an app makes that more dependable.
Yes. Open it in Safari, add it to your home screen from the share menu, and use a keyboard. Command + Enter runs the current file.
No. There is nothing to sign up for.
The link carries a copy of the code. It opens on their side as a temporary preview, and they can save it into their own files. Changes they make never reach your copy.
They are still in the browser you used there. They don't move on their own. Open the old address, download your files or projects from the Files panel, then upload them at coderunner.lab829.com.
Occasional emails when CodeRunner ships something new. No spam.
We only store your email address, use it only for CodeRunner and Lab829 updates, and never share it. Every email has an unsubscribe link, or reply to ask us to delete it.
06 / OPEN A TAB
No account, nothing to install, and your code stays on your device.