AG-UI is an open, lightweight protocol that standardizes how AI agents connect to user-facing applications. Instead of every agent framework inventing its own streaming format, AG-UI defines an event-based interface for agent runs, tool calls, state updates, and human-in-the-loop interactions. Created by the CopilotKit team, it has over 16,000 stars on GitHub and was actively developed in October 2026.
Building a great frontend for an agent is surprisingly hard: responses stream in, tools fire, state changes, and sometimes the agent needs a human decision mid-run. AG-UI gives all of that one shared language. Agents emit a standard stream of events, and any AG-UI-compatible frontend can render progress, show tool activity, sync shared state in both directions, and pause for approvals. It is framework-agnostic, works over standard web transports, and ships with SDKs and integrations for popular agent frameworks, so teams can swap backends without rebuilding their UI.
AG-UI is a free, open protocol under the MIT license. Anyone can implement it in their agent or frontend without fees or royalties.
AG-UI is for developers building products on top of AI agents who need responsive, interactive frontends rather than plain chat boxes. If you are wiring an agent into a real application with live state and user approvals, AG-UI saves you from inventing the plumbing yourself.