What problem does it solve? Python codebases often accumulate tangled dependencies, god classes, deep inheritance hierarchies, and unclear module ownership that make changes risky and reviews painful. This Skill provides structured design guidance for defining explicit module contracts, separating concerns, and planning safe refactors. ## Core Features & Use Cases - Module Boundary Design: Enforces explicit ownership of data, invariants, and public interfaces so modules stay independently understandable and evolvable. - Functional Core / Imperative Shell: Separates deterministic business logic from side effects like I/O, logging, and network calls to improve testability. - Safe Refactor Planning: Sequences structural changes separately from behavior changes, with characterization tests and reversible increments. - Use Case: When reviewing a service where business logic is mixed with database calls and a god class spans multiple concerns, use this Skill to propose a composition-based split with clear ownership boundaries and a stepwise migration plan. ## Quick Start Ask the assistant to review your Python package structure and propose a refactoring plan using the python-design-modularity skill.
