Surface design forces and lay out the option space — including framework defaults, scaffolds, and deferring — before committing to Clean Architecture, DDD, or any heavier pattern. Produces a Design Analysis Memo at the start of /write or /refactor. Make sure to use this skill whenever the user starts a non-trivial feature, restructures code, or asks "do we really need Clean Architecture / DDD / pattern X here".
Write tests using TDD (Red-Green-Refactor) and AAA pattern. Use for every new feature, behavior change, or bug fix. Covers unit, integration, and E2E test selection. Make sure to use this skill whenever the user asks to add tests, fix a bug (tests should come first), implement a feature with test coverage, or asks about what kind of tests to write — even for small one-line changes or trivial-looking fixes.
Safely restructure code without changing behavior using Extract Method, Rename, Move Method techniques. Use when preparing code for new features, improving code quality incrementally, cleaning up messy code, reducing duplication, or simplifying complex logic. Make sure to use this skill whenever the user mentions refactoring, cleaning up code, making code more readable, splitting large files or methods, or removing code smells.
Plan how a system is structured — which layers, modules, or contexts exist and how code is laid out — driven by the forces at play, not by a fixed pattern. The default is to add no extra structure; structure is introduced only when complexity calls for it, and the chosen shape (Clean Architecture, DDD, DCI, or another) is judged in the moment. Use this skill when following a recorded structure in docs/architecture.md, or when deciding the structural shape for a non-trivial feature, a new module, or a restructuring — especially after a design-forces memo recommends a layered or partitioned structure.
Model business domains using DDD patterns: Entity, Value Object, Aggregate, Domain Event. Use when implementing business logic, defining domain concepts, or designing aggregate boundaries. Make sure to use this skill whenever the user works on business rules, creates domain objects, discusses bounded contexts, models workflows or processes, or asks about entity vs value object distinctions — even for simple CRUD features that involve domain invariants.
Apply SOLID, KISS, DRY, YAGNI principles to code design decisions. Use when building new features from scratch and need to decide on class structure, interface boundaries, or dependency direction. Make sure to use this skill when the user faces design trade-offs, asks about SOLID principles, debates whether to abstract or keep things simple, or needs to evaluate competing design approaches — but not for code smell detection (use refactoring skill instead).
Design database schemas and API contracts at system boundaries. Use when creating or modifying database tables, API endpoints, or data serialization formats. Make sure to use this skill whenever the user adds database migrations, designs REST/GraphQL APIs, creates DTOs, defines request/response shapes, or works on data serialization — even for adding a single column or endpoint.
Prevent security vulnerabilities through threat modeling, trust boundary analysis, and defense in depth. Use when writing code that crosses trust boundaries, handles authentication or authorization, processes external input, manages secrets, or stores sensitive data. Make sure to use this skill whenever the user works on login flows, processes data from external sources, builds interfaces between systems, manages credentials, or writes code that moves data across trust zones — even for seemingly simple changes like accepting a new parameter or calling an external service.