Build production-like prototypes from Figma and real data with Cursor

Blair Metcalf, principal UX engineer at Reddit, built an internal platform called Reddit Proto so designers and product managers can make working prototypes without using Git. A desktop app creates the repo, branch and scaffold behind the scenes. People leave annotations on the prototype, and the harness bundles each one with the component it points at, the design-system guidance and the user's intent before handing it to Cursor to make the edit. A custom MCP server maps Reddit's tokens and components to production code so Cursor picks the right ones. Prototypes sign in with the viewer's real Reddit account, so feeds and communities show real content. A separate flow takes a Figma link, maps each element to production components and writes a PRD with acceptance criteria for engineering.

Metcalf reports about 700 prototypes built and full adoption across Reddit's UX and product teams. Some of the strongest users are a visual designer and an animator with no engineering background. Leaders review prototypes built on real components and their own data, which he says cut the back and forth over how things would be implemented. With that many prototypes, finding them became its own problem, and the team is building a searchable console with tags and filters.

Metcalf credits the design-system MCP, not the model, for reliable output: Cursor only builds on-brand screens because the team mapped its components to code first. The account comes from a newsletter summary of his podcast episode; it gives adoption numbers but no figures on time saved or cost.