---
title: "Agent-User Interaction Protocol (AG-UI)"
description: "AG-UI, or Agent-User Interaction Protocol, is an open event-based protocol for connecting AI agents to user-facing applications. It standardizes how agent state, messages, tool events, UI intents, and user interactions move between an agent backend and a frontend."
canonical_url: "https://promptmetheus.com/resources/llm-knowledge-base/agent-user-interaction-protocol-ag-ui"
---

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AG-UI, or Agent-User Interaction Protocol, is an open event-based protocol for connecting [AI agents](https://promptmetheus.com/resources/llm-knowledge-base/ai-agent) to user-facing applications. It standardizes how agent state, messages, tool events, UI intents, and user interactions move between an agent backend and a frontend.

AG-UI addresses a different boundary than the [Model Context Protocol (MCP)](https://promptmetheus.com/resources/llm-knowledge-base/model-context-protocol-mcp) or the [Agent2Agent Protocol (A2A)](https://promptmetheus.com/resources/llm-knowledge-base/agent2agent-protocol-a2a). MCP connects agents to tools and data. A2A connects agents to other agents. AG-UI connects agents to the interactive application surface where a user can see progress, steer work, approve actions, or interact with generated UI.

Typical AG-UI use cases include:

- streaming model output and tool events into an application;
- rendering agent progress, plans, and intermediate work;
- exposing human-in-the-loop approvals;
- synchronizing shared state between frontend and agent runtime;
- supporting [generative UI](https://promptmetheus.com/resources/llm-knowledge-base/generative-ui); and
- allowing users to interrupt, edit, retry, or redirect a long-running task.

The protocol is useful because agent applications are not simple request-response systems. Agents may run for minutes, call tools repeatedly, branch into sub-agents, and need user input before continuing. A stable interaction protocol makes those workflows easier to debug and reuse across frameworks.

Security and product design still matter. A client should make clear which agent is acting, what action is pending, which data is being shown, and whether a user approval changes external state.

The [AG-UI documentation](https://docs.ag-ui.com/) describes AG-UI as the event-based protocol for connecting agentic frontends with agentic backends.

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