AG-UI Protocol: Stream AI Agents Into Your Frontend

AI agents stream tokens, call tools, update shared state, and pause for human input — none of that fits the request/response model your REST APIs were built for. AG-UI is the open, event-based protocol that fixes that. It's a thin wire format with ~16 standard event types that any agent backend (Claude, LangGraph, CrewAI, Pydantic AI, Mastra) can emit and any frontend can consume. As of May 2026 it has 13k+ GitHub stars and first-party integrations across Microsoft, Google ADK, AWS Strands, and more.

Think of it as the third leg of the agentic protocol stack: MCP connects agents to tools, A2A connects agents to other agents, and AG-UI connects agents to your users. This guide gets you a streaming agent → FastAPI server → terminal client in under 50 lines of code, then shows you how to swap the terminal for React.