List the catalog of software-design concepts, optionally filtered by kind. Returns each concept's slug, name, category, and one-line summary.

Return an authoritative explanation of one design principle or GoF pattern: intent, when to use it, trade-offs, participants, and related concepts. Accepts a slug, full name, or alias (e.g. "SRP", "factory").

Generate a language-agnostic pseudo-code skeleton for a GoF pattern, showing its participants and how they collaborate. Optionally rename roles to your domain (e.g. Product -> Notification). Translate the result into your target language.

Scan a code snippet for heuristic design smells (long method, large class, long parameter list, deep nesting, duplication, large file). Each finding maps to the principle it hints at plus a suggested refactor. HEURISTICS ONLY — hints, never verdicts; a clean run does not certify good design.