AG-UI Protocol
Also called AG-UI, Agent-User Interaction Protocol
An open protocol that streams events between an AI agent's backend and a user-facing app, so the interface can show progress, tool use and results as they happen.
What is the AG-UI protocol?
AG-UI (Agent-User Interaction) is an open protocol for connecting an AI agent to the application a person uses. It defines a standard set of events the agent sends while it works, so the interface can update live instead of waiting for a single final answer.
How does it work?
The agent backend streams events such as text as it is generated, tool calls starting and finishing, and changes to shared state. The front end listens and renders them. The user's input and approvals travel back the same way. It sits alongside MCP, which connects agents to tools, and the Agent2Agent protocol, which connects agents to each other.
What is a simple example?
In a travel-planning app, you see the agent search flights, then draft an itinerary, then pause to ask which hotel you prefer, all updating on screen as it happens.
Why does it matter?
Agents take time and make decisions along the way. A standard event format lets different agent backends and front ends work together while keeping the user informed and in control.