Owen Williams, a design manager at Stripe, sat down with Claire Vo on How I AI to walk through Protodash, the internal prototyping tool he has spent the last eighteen months building. What sticks is what Protodash has done to the handoff. Williams, describing the Radar fraud-detection team:
They literally have a pull request of a prototype that I had I see an engineer working on and I’m like this has never happened ever in my career as a design manager. They’re like “I’ll just use the prototype as the source of truth” and they can just take it and do that. There’s a huge change — not having to red line a Photoshop file or all of that stuff.
That’s the part that matters. The prototype is the code, in the same components, ready to be picked up. Protodash gets there by constraining generation: a bundle of Cursor rules, a router and chrome scaffold, and Stripe’s design system (Sail) exposed via an MCP server. The off-the-shelf tools—v0, Cursor by itself, Claude Design—produce what Williams calls “blurple slop” because they hallucinate components. Wire the generator to the actual system and the output stops looking like a Tailwind demo and starts looking like Stripe.
The fidelity jump changes the room, too:
It’s sort of been this very transformative thing because all of a sudden I’m sitting in these design reviews and it’s so convincing that I’m like, is this the real product or am I looking at something fake?
This is what Tara Tan predicted: the moat in AI design tooling is the design-system graph, and whoever makes that graph machine-readable for agents wins the enterprise. Stripe just did it, internally, with a homemade stack, meaning it’s really an uphill battle for anyone trying to make a generic tool for this use case.
The interesting thing is who shows up to use it. Williams says Protodash is now used more by PMs than designers; PMs paste a PRD from Google Docs and get back a working flow before designers are pulled in. That tracks with the Figma Make case studies — PM-led prototyping isn’t theoretical anymore.
Williams is clear-eyed about what the tool can’t do:
How can I make sure that the tool knows enough to be dangerous? It gets to 80%. But like that taste, that craft is like, that’s why designers will always exist, in my opinion. Like they know how to elevate the experience. Like this thing knows how to use the components. The components are well designed, but it’s not going to be perfect. And we are here to steer them.
