@@ -1,5 +1,7 @@
 # Unreleased
 
+- Add [`cognitive_complexity`](https://github.com/leancodepl/flutter_corelibrary/tree/master/packages/leancode_lint#cognitive_complexity), which reports functions whose cognitive complexity is over a configurable maximum (15 by default). It is disabled by default.
+- Require `analyzer: '>=13.1.0 <15.0.0'`
 - Fix [`use_design_system_item`](https://github.com/leancodepl/flutter_corelibrary/tree/master/packages/leancode_lint#use_design_system_item) not reporting forbidden items used via dot shorthands (e.g. `.new()`, `.fromARGB()`, `.staticMember`).
 
 # 27.0.0
 
@@ -595,6 +595,53 @@ final plugin = LeanCodeLintPlugin(
 
 </details>
 
+<details>
+<summary><code>cognitive_complexity</code></summary>
+
+### `cognitive_complexity`
+
+**AVOID** functions that are hard to follow.
+
+Reports functions, methods, constructors and closures whose
+[Cognitive Complexity](https://www.sonarsource.com/docs/CognitiveComplexity.pdf)
+is over the maximum (15 by default). Each `if`, `switch`, `?:`, loop and `catch`
+costs 1, plus 1 for each level it is nested at; each `else` and each run of `&&`
+or `||` costs 1. Unlike the original metric:
+
+- a closure is scored on its own, and only the first level of nested functions
+  adds a nesting level, so a `test` isn't penalized for sitting in a `group`
+- a collection `if` and null-aware operators (`?.`, `??`, `!`, ...) cost nothing
+
+The full scoring table and the reasons for each deviation are in the
+[rule's documentation](./lib/src/lints/cognitive_complexity.dart).
+
+#### Configuration
+
+Disabled by default. Enable it in `analysis_options.yaml`:
+
+```yaml
+plugins:
+  leancode_lint:
+    version: ^27.1.0
+    diagnostics:
+      cognitive_complexity: true
+```
+
+The maximum is configured via `LeanCodeLintConfig.cognitiveComplexity`:
+
+```dart
+import 'package:leancode_lint/plugin.dart';
+
+final plugin = LeanCodeLintPlugin(
+  name: 'my_lints',
+  config: LeanCodeLintConfig(
+    cognitiveComplexity: CognitiveComplexityConfig(maximum: 30),
+  ),
+);
+```
+
+</details>
+
 <details>
 <summary><code>hook_widget_does_not_use_hooks</code></summary>
 
 
@@ -17,6 +17,9 @@ final class const LeanCodeLintConfig({
 
   /// Configuration for the `bloc_related_class_naming` rule.
   final BlocRelatedClassNamingConfig blocRelatedClassNaming = const .new(),
+
+  /// Configuration for the `cognitive_complexity` rule.
+  final CognitiveComplexityConfig cognitiveComplexity = const .new(),
 });
 
 /// Configuration for the `bloc_related_class_naming` rule.
@@ -34,6 +37,12 @@ class const BlocRelatedClassNamingConfig({
   final String presentationEventSuffix = 'PresentationEvent',
 });
 
+/// Configuration for the `cognitive_complexity` rule.
+///
+/// [maximum] is the highest cognitive complexity a function may have. The
+/// default, 15, is SonarSource's and Biome's.
+class const CognitiveComplexityConfig({final int maximum = 15});
+
 class const CatchParameterNamesConfig({
   final String exception = 'err',
   final String stackTrace = 'st',
 
@@ -14,6 +14,7 @@ import 'package:leancode_lint/src/lints/avoid_single_child_in_multi_child_widget
 import 'package:leancode_lint/src/lints/bloc_related_class_naming.dart';
 import 'package:leancode_lint/src/lints/bloc_subclasses_naming.dart';
 import 'package:leancode_lint/src/lints/catch_parameter_names.dart';
+import 'package:leancode_lint/src/lints/cognitive_complexity.dart';
 import 'package:leancode_lint/src/lints/constructor_parameters_and_fields_should_have_the_same_order.dart';
 import 'package:leancode_lint/src/lints/hook_widget_does_not_use_hooks.dart';
 import 'package:leancode_lint/src/lints/missing_equatable_props.dart';
@@ -62,6 +63,9 @@ final class LeanCodeLintPlugin({
         CatchParameterNames(config: config.catchParameterNames),
       )
       ..registerWarningRule(AvoidCatchError())
+      ..registerLintRule(
+        CognitiveComplexity(config: config.cognitiveComplexity),
+      )
       ..registerWarningRule(AvoidBuildContextInBlocs())
       ..registerWarningRule(AvoidConditionalHooks())
       ..registerWarningRule(AvoidDirectCollectionEqualityChecks())