# Simulator Extensions

A simulator extension is a static web application that complements a traditional MakeCode extension. When you add an extension containing a simulator extension to your MakeCode project, the simulator extension is loaded into a separate iframe within the MakeCode editor. This enables extensions to display custom UI when the project is running.

> [!IMPORTANT]
> Simulator extensions are only supported for [Approved Extensions](./approval.md), and they must go through an additional approval process. The MakeCode team reserves the right to approve or decline simulator extensions at their discretion. We strongly recommend consulting with the MakeCode team before investing time and resources into creating a simulator extension.

## Example simulator extensions

* [pxt-simx-sample](https://github.com/microsoft/pxt-simx-sample)
* [pxt-arcadeshield](https://github.com/microsoft/pxt-arcadeshield)
* [microbit-robot](https://github.com/microsoft/microbit-robot)
* [pxt-jacdac](https://github.com/microsoft/)

## Creating a simulator extension

Refer to the [pxt-simx-sample](https://github.com/microsoft/pxt-simx-sample) project for detailed instructions.

