Why Reddit built its own AI prototyping tool | Blair Metcalf

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Why Reddit built its own AI prototyping tool | Blair Metcalf

🎙️ Reddit’s principal UX engineer shows how a custom Figma MCP and Cursor pipeline takes any designer from blank slate to shareable, production-shaped prototype in minutes—no Git required

Claire Vo

Oct 26, 2026

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Transcript

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.

Listen or watch on

YouTube

,

Spotify

, or

Apple Podcasts

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 sponsoring the podcast, email

[email protected]

.

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How I AI

How I AI, hosted by Claire Vo, is for anyone wondering how to actually use these magical new tools to improve the quality and efficiency of their work. In each episode, guests will share a specific, practical, and impactful way they’ve learned to use AI in their work or life. Expect 30-minute episodes, live screen sharing, and tips/tricks/workflows you can copy immediately. If you want to demystify AI and learn the skills you need to thrive in this new world, this podcast is for you.

How I AI, hosted by Claire Vo, is for anyone wondering how to actually use these magical new tools to improve the quality and efficiency of their work. In each episode, guests will share a specific, practical, and impactful way they’ve learned to use AI in their work or life. Expect 30-minute episodes, live screen sharing, and tips/tricks/workflows you can copy immediately. If you want to demystify AI and learn the skills you need to thrive in this new world, this podcast is for you.

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