Design software architecture around business domain models. Use when starting a new project, creating module structure, defining entities and their relationships, or when the user mentions DDD, domain model, bounded context, aggregates, or business logic architecture.
Develop software from detailed specifications that serve as contracts. Use when building APIs, integrations, complex features with multiple conditions, or when the user provides OpenAPI specs, JSON schemas, detailed requirements, or mentions SDD, specification, contract-first development.
Write code by first creating tests that define expected behavior. Use when implementing business logic, algorithms, utilities, or when the user provides test cases, mentions TDD, asks to write tests first, or wants verifiable code generation.