Use whenever writing, modifying, or reviewing tests in this project. Defines the expected style for unit tests and API controller (slice / narrow integration) tests. Stack-agnostic — examples are in Kotlin, but principles apply to any language/framework.
Use when writing any new code or feature to enforce the TDD red-green-refactor cycle.
Use whenever writing, modifying, or reviewing UI tests in React projects. Defines naming, structure, query priority, render conventions, and mocking patterns for component and hook tests. Framework-agnostic on the component library; assumes React + Testing Library + a modern test runner (Vitest or Jest). Inherits the high-level principles from [[testing]].
Clean Architecture conventions — Vaughn Vernon-shaped folder structure (aggregate-per-package on the write side, peer query/ folder on the read side, application/ holding UseCases not Services), dependency rules, design patterns, repository conventions, and code conventions. Invoke this skill when you need to know where layers live, what can import what, or how to structure production code.
HTTP / REST boundary rules — controller shape, REST URL design, request/response modeling, validation ownership, status codes, HTTP semantics, idempotency. Stack-agnostic. Invoke this skill when designing or reviewing a new HTTP endpoint, modeling request/response DTOs or error payloads, choosing HTTP methods or status codes, or drawing the line between input-format validation and domain rule enforcement.
CQRS conventions — when to split write side (Repository + UseCase) from read side (Query). Invoke when planning a new port, deciding whether a UseCase is needed, naming a port, shaping a read model, choosing where to place it, or evaluating whether a class is a pass-through middleman. Stack-agnostic — example is in Kotlin.
Use when working on untested, tangled, or outdated code — adding tests to a system that has none, untangling shared mutable state, replacing deprecated patterns, language/framework migrations, dependency rewrites. Follows Michael Feathers' "Working Effectively With Legacy Code" approach. Language-agnostic.
Create an Architecture Decision Record (ADR) in docs/adr/. Describe the decision and context, or have a conversation to refine it.