Jeremiah Lowin

MCP Apps are a big deal: tools can now return dashboards, forms, and visualizations directly in the conversation. But somebody (or their agent) has to write those UIs. Fortunately, most of those UIs don't need to be designed from scratch; they can be composed from existing components. In that case, what you really need is a DSL that's token-efficient, streaming-compatible, and has a shallow learning curve. Surprisingly, the best one turns out to be... Python. In this talk, I'll introduce Prefab, a generative UI library that uses Python to compose fully interactive React applications from production components, now natively integrated into FastMCP. I'll demo real use cases, walk through the design, and show where this approach works and where it doesn't. No JavaScript will be harmed.