Why Reddit built its own AI prototyping tool | Blair Metcalf
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: Why Reddit built its own prototyping harness How designers share prototypes with leadership safely Why real Reddit data beats mock data How one annotation becomes a code edit in Cursor What a “feature capsule” is Why Blair built a “Rosetta stone” Blair’s surprising fix when AI goes sideways Who turned out to be Reddit’s best prototypers — This entire episode is brought to you by: Firecrawl —Give your AI agents web data and beyond — In this episode, we cover: (00:00) Introduction to Blair (02:31) Reddit Proto demo (09:15) Annotations to Cursor: the targeted edit workflow (11:19) Internal deployment and adoption (14:14) How leadership reviews and gives feedback (15:52) Engineering handoff and the feature capsule (17:50) How the custom MCP was built (21:41) Quick recap (24:55) Lightning round and final thoughts — Tools referenced: • Cursor: https://www.cursor.com/ • Figma: https://www.figma.com/ • Figma MCP (Figma’s Model Context Protocol integration): https://www.figma.com/mcp-catalog/ • Code Connect (Figma’s code mapping tool): https://www.figma.com/developers/code-connect • Gemini: https://gemini.google.com/ • ChatGPT: https://chatgpt.com/ • Vercel (referenced as inspiration for internal deploy infra): https://vercel.com/ — Other references: • Reddit: https://www.reddit.com/ • Kubernetes: https://kubernetes.io/ — Where to find Blair Metcalf: LinkedIn: https://www.linkedin.com/in/jblairmetcalf — Where to find Claire Vo: ChatPRD: https://www.chatprd.ai/ Website: https://clairevo.com/ LinkedIn: https://www.linkedin.com/in/clairevo/ X: https://x.com/clairevo — Production and marketing by https://penname.co/ . For inquiries about spon
