Owen Williams at Stripe built Protodash, an internal AI prototyping studio that generates working Stripe dashboard flows inside dev boxes. It fixes the blurple slop from generic tools by teaching Cursor and MCPs the Stripe design system, then layering review mode, variant testing, AI annotations, and even self-testing on top. PMs now build as much as designers, pushing a demos not memos review culture. Bonus nod: lo-fi modes and Comic Sans for WIP made the case for lowering fidelity when it helps.

  • Protodash runs in dev boxes, removing local setup hassles.
  • Cursor rules and MCPs bind AI to Stripe's design system.
  • Architecture uses React Router and design system components.
  • Variant testing and self-testing catch UI issues early.
  • PMs emerge as heavy users, speeding handoff to engineering.