How to add Lint rules in Flutter

As your team and project grow, you might need to enforce some coding rules to make your code go the same direction. Luckily, adding custom lint rules in Flutter is very easy (If you use a new Flutter version).

Flutter version 2.3.0-12.0.pre or newer

Projects created with flutter create using Flutter version 2.3.0-12.0.pre or newer come with pre-installed package:flutter_lints. This package contains a recommended set of lints for Flutter apps to encourage good coding practices.

To add your custom rules:

1. Open the analysis_options.yaml file in the project root folder. This file is created for you by the flutter create command. You should see a boilerplate similar to this.

# This file configures the analyzer, which statically analyzes Dart code to
# check for errors, warnings, and lints.
#
# The issues identified by the analyzer are surfaced in the UI of Dart-enabled
# IDEs (https://dart.dev/tools#ides-and-editors). The analyzer can also be
# invoked from the command line by running `flutter analyze`.

# The following line activates a set of recommended lints for Flutter apps,
# packages, and plugins designed to encourage good coding practices.
include: package:flutter_lints/flutter.yaml

linter:
  # The lint rules applied to this project can be customized in the
  # section below to disable rules from the `package:flutter_lints/flutter.yaml`
  # included above or to enable additional rules. A list of all available lints
  # and their documentation is published at
  # https://dart-lang.github.io/linter/lints/index.html.
  #
  # Instead of disabling a lint rule for the entire project in the
  # section below, it can also be suppressed for a single line of code
  # or a specific dart file by using the `// ignore: name_of_lint` and
  # `// ignore_for_file: name_of_lint` syntax on the line or in the file
  # producing the lint.
  rules:
    # avoid_print: false  # Uncomment to disable the `avoid_print` rule
    # prefer_single_quotes: true  # Uncomment to enable the `prefer_single_quotes` rule

# Additional information about this file can be found at
# https://dart.dev/guides/language/analysis-options

2. Add your rules in analysis_options.yaml under the rules key. Here is an example where I add an extra prefer_relative_imports rule.

include: package:flutter_lints/flutter.yaml

linter:
  rules:
    - prefer_relative_imports

You can find all available rules here.

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Old Flutter version

If you are on a project that was created with an old Flutter version, you have to do a little setup.

You need to do two things:

1. Add a dev_dependency on package:flutter_lints to your project's pubspec.yaml by running the following command in the project's root directory.

flutter pub add --dev flutter_lints

2. Create an analysis_options.yaml file in the root directory of your project with the following content:

include: package:flutter_lints/flutter.yaml

linter:
  rules:

And now you can start filling in your own rules.