Free AI-powered tools to validate designs against 168 research-backed UX principles. Cursor, v0, and Claude generate beautiful interfaces but silently break UX fundamentals — Hick's Law violations, cognitive overload, missing feedback loops. 5 free tools: AI Validator, UX Smell Detector, Flow Checklists, AI Prompts (600+), Parts Checklist. No signup needed. Principles Library ($29/yr) unlocks all 168 principles with examples and prompts. Backed by 2,098+ citations. EN/ES.