Ruben Casas

Declarative UI Is Emerging as the Practical Path for Agent Interfaces

Ruben Casas of Postman argues that agent interfaces have not caught up with the frontend code models can now generate. In his talk, he contrasts static component systems with declarative UI, where an LLM produces JSON or YAML for a renderer, and fully generative UI, where the model writes HTML, CSS and JavaScript directly. Casas says declarative UI is probably the right balance today, while MCP apps matter because their sandboxing offers a way to contain runtime-generated interfaces.