To update your code to follow the Dart formatting guidelines, use the dart format command. This formatting follows what you get when using an IDE or editor with Dart support.

To reformat one or more Dart files, provide a list of paths to the desired files or directories.

Provide the path to one file or directory. If you pass a directory path, dart format recurses into its subdirectories as well.

Example: To format all the Dart files in or under the current directory:

To specify multiple files or directories, use a space-delimited list.

Example: To format all Dart files under the lib directory, plus one Dart file under the bin directory:

dart format lib bin/updater.dart

By default, dart format overwrites the Dart files.

• To not overwrite the files, add the --output or -o flag.
• To get the contents of the formatted files, add -o show or -o json.
• To see only which files would change, add -o none.

dart format -o show bin/my_app.dart

To make dart format return an exit code when formatting changes occur, add the --set-exit-if-changed flag.

• If changes occur, the dart format command returns an exit code of 1.
• If changes don't occur, the dart format command returns an exit code of 0.

Use exit codes with continuous integration (CI) systems so they can trigger another action in response to the exit code.

dart format -o none --set-exit-if-changed bin/my_app.dart

Many editors with Dart support can automatically format your code when you save a file.

To enable formatting on save in VS Code, add the following entry to your settings.json file:

{
  "[dart]": {
    "editor.formatOnSave": true
  }
}

To enable formatting on save in JetBrains IDEs, including IntelliJ IDEA and Android Studio, follow their instructions on how to Automatically reformat code on save.

dart format makes the following formatting changes:

• Removes whitespace.
• Wraps every line to 80 characters long or shorter.
• Adds trailing commas to any argument or parameter list that splits across multiple lines, and removes them from ones that don't.
• Might move comments before or after a comma.

To learn more about best practices for writing and styling Dart code, check out the Dart style guide.

When you run dart format, the formatter defaults to 80 character line length or shorter. Configure the formatter's behavior by adding a top-level formatter section to the analysis_options.yaml file.

Configure the line length for your project:

formatter:
  page_width: 123

With the analysis options file typically at the root, the configured line length will apply to everything in the package.

By default, dart format adds or removes trailing commas based on whether the construct splits across multiple lines. To force a construct to split even when it fits on one line, configure the formatter to preserve trailing commas:

formatter:
  trailing_commas: preserve

When enabled, adding a trailing comma to an argument list, parameter list, or other constructs, forces the formatter to split it across multiple lines, even if it fits on one line. This provides manual control over line breaks for specific constructs. This gives you manual control over line breaks for specific constructs.

Configure an individual file's line length, overriding the analysis options, by adding a marker comment at the top of the file, before any other code:

// dart format width=123

To learn about additional command-line options, use the dart help command or see the documentation for the dart_style package

Check out the formatter FAQ for more context behind formatting decisions.