google/a2ui

A2UI, which stands for Agent-to-User Interface, is a Google open-source project that lets an AI agent build a real, interactive user interface for the user to look at, not just text. Generative AI is good at writing words and code, but agents often struggle to show rich screens like forms, cards, sliders, or date pickers, especially when the agent is running on a different server than the user's app. A2UI fixes that by giving agents a standard way to describe a UI in JSON. The README marks the project as version 0.8, an early public preview, with the specification still evolving. The basic idea is that the agent sends a small JSON document describing what UI it wants, and the client application renders that JSON using its own native components, whether the client is built in Flutter, Angular, Lit, React, SwiftUI, or something else. The same JSON can therefore appear on many different platforms. The project's design choices are listed plainly. Security comes first: A2UI is data, not code, and the client only allows components from a trusted catalog it controls. The format is meant to be easy for large language models to generate piece by piece, so the UI can update progressively during a conversation. The structure is separated from the implementation, so the agent does not need to know which framework the client uses. A registry pattern lets developers attach custom components, including secure iframes for legacy content, with their own sandboxing rules. The README lists three example use cases: an agent generating a custom form for a booking, an orchestrator agent passing a job to a remote specialist agent that returns a UI to show inside the main chat, and enterprise agents producing approval dashboards or charts on demand. The flow is split into generation, transport over protocols like A2A or AG UI, parsing by the A2UI Renderer, and finally rendering by mapping abstract types to real widgets. Getting started options include a five-minute Restaurant Finder demo that uses a Gemini-powered Python agent and a Lit renderer, an integration with CopilotKit for React apps, a visual A2UI Composer and Widget Builder, and a Theater that steps through pre-built streaming scenarios across Lit, React, and Angular. A Flutter SDK called GenUI also uses A2UI underneath.