How Reddit’s designers build ultra-realistic prototypes with Figma + Cursor

Blair Metcalf is the principal UX engineer at Reddit and the builder of Reddit Proto, the company’s in-house vibe-coding harness. With a design system MCP that maps Reddit’s product language to production code, Proto has reached 100% adoption across Reddit’s UX and product org, and more than 700 prototypes are live on it. *What you’ll learn:* 1. Why Reddit built its own prototyping harness 2. How designers share prototypes with leadership safely 3. Why real Reddit data beats mock data 4. How one annotation becomes a code edit in Cursor 5. What a “feature capsule” is 6. Why Blair built a “Roset