What problem does it solve? Codebases often accumulate shallow modules whose interfaces are nearly as complex as their implementations, making code hard to test, navigate, and change. This Skill provides a shared vocabulary and design principles for creating deep modules that hide complexity behind small interfaces. ## Core Features & Use Cases - Deep Module Vocabulary: Defines precise terms (module, interface, seam, adapter, depth, leverage, locality) so teams and AI agents discuss design consistently. - Dependency-Aware Deepening: Classifies dependencies (in-process, local-substitutable, remote-owned, true external) and prescribes ports-and-adapters strategies for each, with replace-don't-layer testing guidance. - Design It Twice Workflow: Spawns parallel sub-agents to produce radically different interface designs, then compares them on depth, locality, and seam placement. - Use Case: When refactoring a cluster of shallow service classes, use this Skill to identify the right seam, define a port with production and in-memory test adapters, and consolidate logic into one deep module tested through its interface. ## Quick Start Ask the AI to review a module in your codebase and propose a deeper interface using the codebase-design vocabulary.
