Design sprint with vibe coding and user-centered prototyping
A product team that could run its own design sprints by day three
About
Vanilla Steel is Europe's largest independent B2B steel marketplace — a Berlin startup connecting 500+ suppliers and 3,000+ buyers, backed by ~$4M in seed funding and an EU grant, with clients including ArcelorMittal. As it scaled, the product team was moving fast but getting disconnected from the real workflows of both buyers and sellers.
Challenge
The team had validated the marketplace and built an MVP, but as they scaled they were shipping features without deeply understanding the friction across buyer and seller journeys — RFQ (request-for-quote) coordination among them. They needed a repeatable way to turn user research into working prototypes fast, rather than debating in design docs.
Solution
Ran a design sprint at the launchlabs Berlin office that shifted the team from assumption-driven feature-building to user-centered rapid prototyping. It opened with fieldwork — interviews with active buyers and sellers to map real RFQ friction — and by day three, with coaching in vibe-coded prototyping, the team was self-organising: sketching, coding and testing with users instead of arguing in documents. They reached a working RFQ quoting prototype to test.
Outcome
The RFQ prototype didn't go to production — and that wasn't the point. By day three the team had stopped waiting for direction and was prototyping with real users on its own, and they left able to run the method without me.
He didn't add a designer to the team — he made the team designers, then left.
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