# Run code

> How code runs in the browser editor - automatic runs, Start Preview, Stop and Reload, running one file, other languages, and loop protection.
> Source: https://playcode.io/docs/classic/run-code - last reviewed 2026-10-09.

In a JavaScript or web project, the preview runs your code by itself: each change rebuilds it, and the console shows what the code prints. In a Python, C, C++, Go or SQL project, you run the code with **Run**.

## Do it yourself

1. Open the project. The preview builds as soon as it opens, unless you turned off **Run on opening**.
2. Edit a file. The preview rebuilds when you stop typing, after the **Live view delay**: 0.1 seconds unless you change it.
3. To build it again by hand, choose the **Reload** button in the preview's toolbar, or press Ctrl+R (Control+R on a Mac).
4. To stop the preview, choose the **Stop** button. To start it again, choose the **Start Preview** button. Stopping clears the build, so the next start builds everything again.
5. To run one file instead of `index.html`, point at the file's icon in the file list: the icon turns into a play button. Click it.
6. In a Python, C, C++, Go or SQL project, choose **Run** in the console's toolbar, or press Ctrl+R. The output appears in the editor.

To start over from nothing, press Ctrl+Shift+R (Control+Shift+R on a Mac): the build is cleared and runs again.

## If it doesn't work

### "No entry point found. Create index.html or click a file to run."

The preview starts from `index.html`. Without it, it tries `index`, `main`, `script`, `src/main` and `src/script`, with a script ending like `.js`, `.ts`, `.jsx` or `.tsx`. Create `index.html`, or choose a file under "Available files to run:".

### "Entry point not found: /about"

The preview's address names a file that does not exist. For `/about`, the preview tries `about`, `about.html` and `about/index.html`. Choose one of the files the message lists.

### "SPA mode is enabled but /index.html not found."

Create `index.html`, or turn off SPA mode. See [SPA mode](/docs/classic/spa-mode).

### "Potential infinite loop: exceeded 1500 iterations."

**Loop protection** stopped a loop that ran more than 1,500 times. If your loop is meant to run longer, like a game loop or a long list, choose **Disable Loop Protection** in the console. Loop protection works only in the preview, never on the published site.

### "Imported module ... is not installed."

The preview shows **Missing Module**. Choose **Install** followed by the package's name. See [Add npm packages](/docs/classic/npm-packages).

### The preview does not change when you type

**Live reload** is off. Choose **Reload**, or turn it on again: see [Turn off automatic runs](/docs/classic/turn-off-auto-run).

### The preview is blank, stuck or frozen

Press Ctrl+Shift+R, or choose **Stop**, then **Start Preview**. For more fixes, see [The preview does not load](/docs/help/preview-does-not-load).

## Limits

- The code runs in your browser. Code that needs a server, files on a disk or Node.js runs in a Cloud app instead: see [Browser and Cloud projects](/docs/build/browser-and-cloud-projects).
- Loop protection stops `for`, `while` and `do` loops, not a recursion that never ends.
- The shortcuts work in the editor only. **Help**, **Keyboard Shortcuts** lists the others.