What problem does it solve? Domain rules often live only in documents, comments, or developers' memory, causing duplicated conditionals, invalid states, and modules organized by technical role instead of concept. This Skill diagnoses where knowledge has leaked out of the code and guides moving it into types, ADTs, and pure functions. ## Core Features & Use Cases - Diagnostic Smell Detection: Identifies eight concrete symptoms of missing domain knowledge, such as duplicated conditionals, boolean-flag state combinations, and modules split by technical role. - Four-Layer Design Framework: Classifies problems into boundary (Parse, don't validate), core (ADT + total functions), placement (Functional Core, Imperative Shell), and dependency (Port & Adapter) layers so the right technique is chosen first. - Executable Specifications: Converts documentation-only rules into single declarations from which behavior is derived, with tests that verify the declaration actually drives the implementation. - Use Case: When a state transition table exists only in a Markdown file and the same conditional is scattered across handlers, use this Skill to model states as a tagged union, declare transitions as data, and derive all conditionals from that single source of truth. ## Quick Start Ask the AI to review a module using functional DDD principles and refactor scattered conditionals and nullable state combinations into ADTs and pure functions.
