Installing and Running the Emulator

If you do not have an iOS or Android phone or tablet, you can still build apps with App Inventor. App Inventor provides a mobile phone emulator, which works just like an Android device but appears on your computer screen. So you can test your apps on an emulator and still distribute the app to others, even through the Google Play Store. Some schools and after-school programs develop primarily on emulators and provide a few iOS or Android phones for final testing.

To use the emulator, you will first need to install some software on your computer (this is not required for testing apps with a mobile device and Wi-Fi). Follow the instructions below for your operating system, then come back to this page to start the emulator

Important: If you are updating a previous installation of the App Inventor emulator/USB software, see How to update the App Inventor emulator software. You can check whether your computer is running the latest version of the software by visiting the test page for the emulator/USB software component, aiStarter.

Step 1. Install the App Inventor Setup Software

Step 2. Launch aiStarter (Windows & GNU/Linux only)

Using the emulator or the USB cable requires the use of a program named aiStarter. This program is the helper that permits the browser to communicate with the emulator or USB cable. The aiStarter program was installed when you installed the App Inventor Setup package. You do not need aiStarter if you are using only the wireless companion.

For Help with aiStarter, see Connection Help.

Step 3. Open an App Inventor project and connect it to the emulator

First, go to App Inventor and open a project (or create a new one -- use Project > Start New Project and give your project a name).

Then, from App Inventor's menu (on the App Inventor cloud-based software at, go to the Connect Menu and click the Emulator option.

Build your project on your computer and test it in real-time on the emulator

You'll get a notice saying that the emulator is connecting. Starting the emulator can take a couple of minutes. You may see update screens like the following as the emulator starts up:

The emulator will initially appear with an empty black screen (#1). Wait until the emulator is ready, with a colored screen background (#2). Even after the background appears, you should wait until the emulated phone has finished preparing its SD card: there will be a notice at the top of the phone screen while the card is being prepared. When connected, the emulator will launch and show the app you have open in App Inventor.

If this is the first time using the emulator after installing it, you will see a message asking you to update. Follow the directions below ("Troubleshooting") to perform the update and reconnect the emulator. You will need update whenever there is a new version of the App Inventor Companion.

For problems with aiStarter, or if the Emulator does not connect, go to Connection Help for information about what might be wrong.

#1 #2 #3 #4

Troubleshooting: Check that the Companion version number in your emulator is the newest one.

If the emulator does not work, it may have an older version of Companion installed. Luckily, this is an easy fix. First, check Companion information in App Inventor. Next, compare the latest Companion version with the one in the emulator.
If the emulator Companion is old, update it using the menu in App Inventor:

Setup complete! You are now ready to build your first app!