AG-UI — Agent-User Interaction Protocol

Overview

AG-UI standardizes how an agent backend talks to a user-facing app. The app POSTs one JSON RunAgentInput (thread id, run id, messages, state, tools, context, forwarded props); the agent answers with a stream of typed events. It sits beside MCP (agents to tools) and A2A (agent to agent). The protocol was created by the CopilotKit team and is implemented by LangGraph, Mastra, CrewAI, Pydantic AI, Google ADK, Microsoft Agent Framework, AWS Strands, Agno, LlamaIndex, AG2 and others. Version 1.0 shipped in September 2026; this skill was checked against @ag-ui/core/client/encoder 1.0.1 and the Python ag-ui-protocol 1.0.0.

There are no @ag-ui/server or @ag-ui/react packages and no AgentServer/useAgent in @ag-ui/*. The SDK packages are @ag-ui/core (types and constants), @ag-ui/client (HttpAgent, subscribers), @ag-ui/encoder (EventEncoder) and, per framework, @ag-ui/langgraph, @ag-ui/mastra and so on. The React layer comes from CopilotKit (@copilotkit/react-core/v2).

Instructions

Event vocabulary

Every event has a type. The families: