Getting Started with Sky

Sky apps are written in Dart. To get started, we need to set up Dart SDK:

Once you have installed Dart SDK, create a new directory and add a pubspec.yaml:

name: your_app_name
  sky: any
  sky_tools: any

Next, create a lib directory (which is where your Dart code will go) and use the pub tool to fetch the Sky package and its dependencies:

  • mkdir lib
  • pub upgrade

Sky assumes the entry point for your application is a main function in lib/main.dart:

import 'package:sky/widgets.dart';

class HelloWorldApp extends App {
  Widget build() {
    return new Center(child: new Text('Hello, world!'));

void main() {
  runApp(new HelloWorldApp());

Execution starts in main, which in this example runs a new instance of the HelloWorldApp. The HelloWorldApp builds a Text widget containing the traditional Hello, world! string and centers it on the screen using a Center widget. To learn more about the widget system, please see the widgets tutorial.

Setting up your Android device

Currently Sky requires an Android device running the Lollipop (or newer) version of the Android operating system.

  • Install the adb tool from the Android SDK:

  • Mac: brew install android-platform-tools

  • Linux: sudo apt-get install android-tools-adb

  • Enable developer mode on your device by visiting Settings > About phone and tapping the Build number field five times.

  • Enable Android debugging in Settings > Developer options.

  • Using a USB cable, plug your phone into your computer. If prompted on your device, authorize your computer to access your device.

Running a Sky application

The sky pub package includes a sky_tool script to assist in running Sky applications inside the SkyShell.apk harness. The sky_tool script expects to be run from the root directory of your application's package (i.e., the same directory that contains the pubspec.yaml file). To run your app, follow these instructions:

  • The first time: ./packages/sky/sky_tool start --install --checked && adb logcat -s sky chromium
  • Subsequent times: ./packages/sky/sky_tool start --checked && adb logcat -s sky chromium

The sky_tool start command starts the dev server and uploads your app to the device. The --install flag installs SkyShell.apk if it is not already installed on the device. The --checked flag triggers checked mode, in which types are checked, asserts are run, and various debugging features are enabled. The adb logcat command logs errors and Dart print() output from the app. The -s sky chromium argument limits the output to just output from Sky Dart code and the Sky Engine C++ code (which for historical reasons currently uses the tag chromium.)

To avoid confusion from old log messages, you may wish to run adb logcat -c before calling sky_tool start, to clear the log between runs.

Rapid Iteration

As an alternative to running ./packages/sky/sky_tool start every time you make a change, you might prefer to have the SkyShell reload your app automatically for you as you edit. To do this, run the following command:

  • ./packages/sky/sky_tool listen

This is a long-running command -- just press ctrl-c when you want to stop listening for changes to the file system and automatically reloading your app.

Currently sky_tool listen only works for Android, but iOS device and iOS simulator support are coming soon.


Sky uses Observatory for debugging and profiling. While running your Sky app using sky_tool, you can access Observatory by navigating your web browser to http://localhost:8181/.

Building a standalone APK

Although it is possible to build a standalone APK containing your application, doing so right now is difficult. If you're feeling brave, you can see how we build the Stocks.apk in examples/stocks. Eventually we plan to make this much easier and support platforms other than Android, but that work still in progress.