The Developer's Guide to the AG-UI Protocol

AG-UI (Agent-User Interaction Protocol) is an open, framework-agnostic standard for streaming AI agent activity to user-facing applications, addressing the difficulty of displaying real-time reasoning, tool calls, state updates, and parallel subagent work across different frameworks and interfaces. Reaching a stable 1.0 specification, it is supported by major companies and integrations including Google, Microsoft, Amazon, Oracle, Anthropic, LangChain, Mastra, and Pydantic AI, with official TypeScript, Python, and .NET SDKs. The protocol connects an application, client SDK, agent endpoint and bridge through transport-independent JSON events, typically sent using Server-Sent Events, while complementing MCP for tools and data and A2A for agent-to-agent communication. Its 31 event types cover runs and steps, streamed text, tool calls and multimodal results, reasoning, synchronized state, live activity, subagents, and custom or raw events, allowing interfaces to react progressively during a run rather than wait for a final response. AG-UI 1.0 adds features such as human-in-the-loop interruptions, token usage reporting, metadata, capabilities declarations, encrypted reasoning support, and backward compatibility that lets older clients ignore unfamiliar events. The guide illustrates implementation through agent endpoints and SDK clients, demonstrates a flight-booking workflow with live UI updates and approval steps, and points developers toward starter tooling, documentation, integrations, an event inspector, and CopilotKit-based clients for web, mobile, and messaging platforms.

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