AG-UI Protocol Skill

Overview

AG-UI (Agent-User Interaction) is CopilotKit's open event-based protocol for agent-to-UI communication. All agent-frontend interaction flows through typed events streamed over SSE (Server-Sent Events) or binary protobuf transport. Agents implement AbstractAgent.run() returning an RxJS Observable<BaseEvent>, and the client SDK handles event application, state management, and message history.

When to Use

• Building a custom agent backend that needs to speak AG-UI
• Implementing AbstractAgent.run() for a new framework integration
• Debugging why events aren't reaching the frontend or arriving malformed
• Understanding event ordering (lifecycle, text, tool calls, state)
• Working with state synchronization (snapshots vs JSON Patch deltas)
• Implementing human-in-the-loop interrupt/resume flows
• Troubleshooting SSE streaming or encoding issues

When NOT to Use