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Check unused l10n

Checks unused Dart class members, that encapsulates the app’s localized values.

An example of such class:

class ClassWithLocalization {
String get title {
return Intl.message(
'Hello World',
name: 'title',
desc: 'Title for the Demo application',
locale: localeName,

Read more about this localization approach in the Flutter docs.

By default the command searches for classes that end with I18n, but you can override this behavior with --class-pattern argument.

To execute the command, run

$ dart run dart_code_metrics:metrics check-unused-l10n lib

# or for a Flutter package
$ flutter pub run dart_code_metrics:metrics check-unused-l10n lib

Full command description:

Usage: metrics check-unused-l10n [arguments] <directories>
-h, --help Print this usage information.

-p, --class-pattern=<I18n$> The pattern to detect classes providing localization
(defaults to "I18n$")

-r, --reporter=<console> The format of the output of the analysis.
[console (default), json]
--report-to-file=<path/to/report.json> The path, where a JSON file with the analysis result will be placed (only for the JSON reporter).

-c, --print-config Print resolved config.

--root-folder=<./> Root folder.
(defaults to current directory)
--sdk-path=<directory-path> Dart SDK directory path.
Should be provided only when you run the application as compiled executable( and automatic Dart SDK path detection fails.
--exclude=<{/**.g.dart,/**.freezed.dart}> File paths in Glob syntax to be exclude.
(defaults to "{/**.g.dart,/**.freezed.dart}")

--no-congratulate Don't show output even when there are no issues.

--[no-]fatal-unused Treat find unused l10n as fatal.

Output example


Use --reporter=console to enable this format.



The reporter prints a single JSON object containing meta information and the unused file paths. Use --reporter=json to enable this format.

The root object fields are

  • formatVersion - an integer representing the format version (will be incremented each time the serialization format changes)
  • timestamp - a creation time of the report in YYYY-MM-DD HH:MM:SS format
  • unusedLocalizations - an array of unused files
"formatVersion": 2,
"timestamp": "2021-04-11 14:44:42",
"unusedLocalizations": [

The unusedLocalizations object fields are

  • path - a relative path of the unused file
  • className - a name of the class that has unused members
  • issues - an array of issues detected in the target class
"path": "lib/src/some/class.dart",
"className": "class",
"issues": [

The issue object fields are

  • memberName - unused class member name
  • offset - a zero-based offset of the class member location in the source
  • line - a zero-based line of the class member location in the source
  • column - a zero-based column of class member the location in the source
"memberName": "someGetter",
"offset": 156,
"line": 7,
"column": 1