Specify and start devices

Learn how to launch Android and iOS virtual devices using the Maestro CLI, identify connected hardware, and target specific devices for local testing.

When managing multiple simulators, emulators, or physical devices, Maestro needs to know which one to target. This guide covers how to spin up new virtual devices using Maestro, find their identifiers, and target specific hardware for your tests.

Start a device

Maestro allows you to create and launch Android emulators or iOS simulators directly from the CLI. These devices are configured to approximate the environment hosted on Maestro Cloud, ensuring your Flows are compatible when you scale up.

To view all available options and configurations available, run:

maestro start-device

Maestro will list the devices, platforms, and OS versions available in the cloud, similar to the following example:

Supported device types: iPhone11 (iOS), Pixel 6 (Android)
      --os-version=<osVersion>
                       OS version to use:
                       iOS: 16, 17, 18
                       Android: 28, 29, 30, 31, 33
      --platform=<platform>
                       Platforms: android, ios

Android

To create and launch a default Android emulator (Pixel 6, Google API 30), run:

maestro start-device --platform android

If the device already exists, Maestro will simply launch it.

Compatibility

The device configurations created by this command are limited to specific OS versions and models supported by Maestro.

iOS

Find the device identifier

Once your devices are running, you need to obtain their unique identifier (ID) to target them specifically.

Android

To list available Android devices, run the following command in your terminal:

adb devices

From the output, locate the device identifier for the device you want to use with Maestro.

iOS

Web

Target a specific device

To run a test on a specific device, use the --device flag. This flag must be provided before the test command.

When running a Flow with the Maestro CLI, you can explicitly define the target device. For example, to run flow.yaml on an iOS simulator with the identifier 5B6D77EF-2AE9-47D0-9A62-70A1ABBC5FA2, use the following command:

maestro --device 5B6D77EF-2AE9-47D0-9A62-70A1ABBC5FA2 test flow.yaml

If you are using Maestro Studio, you can select a device through the interface. At the top of Maestro Studio, click No device connected to see a list of all available devices.

Run tests in parallel (Sharding)

If you have multiple devices running, you can speed up your local execution by "sharding" your tests. This allows you to utilize all available hardware simultaneously. You have two options to use sharding:

• --shard-all

• --shard-split

Maestro Cloud

Maestro Cloud handles device allocation and parallelization automatically. Sharding flags are primarily for local development and local CI runners.

Strategy A: --shard-all

Use this to run the exact same test collection across multiple devices. This is ideal for cross-platform validation or checking for flaky tests.

# Runs the entire .maestro folder on 3 devices at once
maestro test --shard-all 3 .maestro

Strategy B: --shard-split

Use this to divide your suite. If you have 9 tests and 3 devices, Maestro will run 3 unique tests on each device, finishing the run in roughly one-third of the time.

# Splits the test suite into 3 chunks and distributes them
maestro test --shard-split 3 .maestro

You can explicitly specify which devices to use for sharding by passing a comma-separated list to the --device flag. For example, if you have three devices running (emulator-5554, emulator-5555, emulator-5556) but only want to shard across two of them:

maestro test --device "emulator-5554,emulator-5556" --shard-split 2 ./myTests

--shard-all and --shard-split

To use these flags, you must have the required number of devices already booted and ready. If you request 3 shards but only 2 devices are connected, Maestro will return an error.

Screenshots when sharding

When sharding, you're using the same workspace on multiple devices at the same time. Taking a screenshot with the same name will cause overwriting. Look at the available environment variables to differentiate.

- takeScreenshot: "LoginScreen-shard_${MAESTRO_SHARD_INDEX}-device_${MAESTRO_DEVICE_UDID}.png"

Related content

• Maestro CLI commands and options: Full list of available flags and commands.

• Test reports and artifacts: Learn how reports are generated when running in parallel.

• Maestro Cloud: Scale your tests to dozens of devices without managing hardware.