Spec-driven development methodology that transforms feature requests into structured documentation before coding. Use when users want to (1) plan a new software project or feature, (2) create requirements/design/tasks documentation, (3) follow a structured development workflow, (4) break down complex features into trackable tasks. Triggers include phrases like "let's plan this properly", "spec-driven", "create requirements", "design document", "task breakdown", "before we start coding".