Question

The Flutter tooling supports three modes when compiling your app, and a headless mode for testing. This doc explains the three modes and tells you when to use which. For more information on headless testing, see Unit testing.

You choose the compilation mode depending on where you are in the development cycle. Are you debugging your code? Do you need profiling information? Are you ready to deploy your app?

The following describes each mode and when to use it.

Debug

In debug mode, the app is set up for debugging on the physical device, emulator, or simulator. Debug mode means that:

• Assertions are enabled.
• Observatory is enabled, allowing you to use the dart debugger.
• Service extensions are enabled.
• Compilation is optimized for fast development and run cycles (but not for execution speed, binary size, or deployment.)

By default, flutter run compiles to debug mode. Your IDE also supports these modes. Android Studio, for example, provides a Run > Debug… menu option, as well as an triangular green run button icon on the project page. (The menu item shows a pic of the corresponding icon.) The emulator and simulator execute only in debug mode.

Release

Use release mode for deploying the app, when you want maximum optimization and minimal footprint size. Release mode, which is not supported on the simulator or emulator, means that:

• Assertions are disabled.
• Debugging information is stripped out.
• Debugging is disabled.
• Compilation is optimized for fast startup, fast execution, and small package sizes.
• Service extensions are disabled.

The command flutter run --release compiles to release mode. Your IDE also supports these modes. Android Studio, for example, provides a Run > Run… menu option, as well as a green bug icon overlayed with a small triangle on the project page. (The menu item shows a pic of the corresponding icon.)

You can also compile to release mode with flutter build. For more information, see the docs on releasing iOS and Android apps.

Profile

In profile mode, some debugging ability is maintained—enough to profile your app’s performance. Profile mode is disabled on the emulator and simulator, because their behavior is not representative of real performance. Profile mode is similar to release mode, with the following differences:

• Some service extensions, such as the one that enables the performance overlay, are enabled.
• Tracing is enabled, and Observatory can connect to the process.

The command flutter run --profile compiles to profile mode. Your IDE also supports these modes. Android Studio, for example, provides a Run > Profile… menu option.

For more information on these modes, see Flutter’s modes in the Flutter SDK wiki.