The internal AI tool that’s transforming how Stripe designs products | Owen Williams

What It Covers

Owen Williams, design manager at Stripe, built ProtoDash — an internal AI prototyping tool that connects Stripe's design system (Sail) via MCP server to generate realistic, on-brand dashboards in a browser. The tool has shifted design reviews from static Figma JPEGs to clickable, data-rich prototypes used by both designers and PMs.

Key Questions Answered

• •Design system MCP integration: Connect your internal design system to an MCP server and bundle cursor rules that instruct the LLM to query that server before writing any code. This prevents the model from hallucinating generic Tailwind components and instead generates on-brand UI at roughly 90% fidelity from a single prompt, eliminating the "indigo blurple slop" problem common in tools like v0.
• •Dev box deployment over local setup: Hosting prototypes on internal dev boxes rather than local machines solves two problems: designers often lack high-RAM engineering laptops, and shareable URLs replace screen-sharing in design reviews. At Stripe, spinning up a ProtoDash dev box takes under two minutes via a single internal URL, making prototypes immediately clickable by everyone in the room.
• •Data state prototyping in code vs. Figma: Prototyping data-heavy dashboards in code unlocks states that Figma cannot practically replicate — zero data, high volume, internationalized text, different business models (startup vs. enterprise), and error states. What previously required duplicating dozens of Figma frames can now be generated by prompting a single variant request directly in the browser-based tool.
• •Embedded annotation-to-fix pipeline: ProtoDash Studio includes a canvas annotation mode where reviewers click UI elements, leave comments directly on the prototype, and queue all feedback for the LLM to action in one batch. This replaces post-review Google Doc summaries and allows designers to send stakeholders a "fixed" confirmation with receipts immediately after the meeting ends.
• •PM self-service prototyping changes designer relationships: When PMs can generate on-brand prototypes by pasting a PRD link into the chat, they unblock early-stage exploration without waiting for designer availability. Rather than displacing designers, this shifts conversations from staffing arguments to craft elevation — PMs arrive at design reviews with a working baseline, and designers focus on refining quality rather than explaining concepts from scratch.