AG-UI — Agent User Interaction Protocol

AG-UI standardizes the event stream between a long-running agent backend and a user-facing frontend. It is not a widget format. Where MCP Apps answers "how does a tool render a card in a chat host", AG-UI answers "how does my app show what the agent is doing, share state with it, and let the user interrupt".

Built on plain HTTP and WebSockets. Deliberately transport-agnostic and deliberately tolerant of event-shape drift, so existing frameworks can adapt their native formats with minimal work.

Use AG-UI when you own the frontend. Use MCP Apps when someone else's chat host is the frontend. They compose: an MCP Apps View can drive an AG-UI stream inside itself for a long-running sub-task.

Core interface