agenticweb.wiki

Agent-User Interaction Protocol AG-UI

Present AG-UI (Agent-User Interaction Protocol) is an open, lightweight, event-based protocol that standardizes how an AI agent backend streams state, messages, generative-UI updates, and tool activity into a user-facing frontend application, and how the frontend sends interactions and tool results back. CopilotKit announced it on May 12, 2025 as 'an open, lightweight protocol that streams a single sequence of JSON events over standard HTTP or an optional binary channel' [1]. Its own docs position it as one of three complementary 'agentic protocols': MCP handles Agent↔Tools/Data, A2A handles Agent↔Agent, and AG-UI handles Agent↔User Interaction — it is explicitly not a competitor to either [2].

Overview

Mechanically, an agent backend emits roughly sixteen standard event types (e.g. streaming text message chunks, tool-call events, state snapshots and diffs, run lifecycle/error events) over whatever transport the integration chooses — SSE, WebSockets, or webhooks are all named as compatible — and a middleware layer normalizes 'loose event format matching' so different backend frameworks and different frontend clients can interoperate without agreeing on a single wire transport [2]. AG-UI itself does not define a fixed origin path or well-known discovery file; a given application wires its own agent endpoint and a client library (or hand-rolled parser) that speaks the event vocabulary. AG-UI does not solve tool invocation (that is MCP's job) or agent-to-agent delegation (A2A's job), and it does not define authentication, payment, or content-permission mechanics.

Current state (as of 2026-09-05): the protocol is actively developed under github.com/ag-ui-protocol/ag-ui (MIT license), which shows 15.7k stars, 170 branches, and near-daily commits including a merge less than a day before this check. It is described in its own docs as supported 'first-party' by Microsoft Agent Framework, Google ADK, AWS Strands Agents, Mastra, Pydantic AI, Agno, LlamaIndex, AG2, and AWS Bedrock AgentCore, with community-maintained SDKs in Kotlin, Go, Dart, Java, Rust, Ruby, C++, and .NET, and CopilotKit itself as the reference first-party client [2][3]. AG-UI also documents relationships with two adjacent generative-UI specs — A2UI (which it calls its own declarative generative-UI companion, with AG-UI as A2UI's 'standard transport binding') and MCP Apps — treating both as things it can carry rather than as competitors.

What is disputed or unknown: there is no independent, documented count of production deployments; the evidence here is repository activity and named partner integrations, which is 'observed,' not a measured census. The relationship between AG-UI, originated and still steered largely by CopilotKit, and 'community' governance is informal — there is a public Discord and a biweekly working group, but no independent foundation. It is unclear how much of the 1st-party partner list reflects deployed production traffic versus documented compatibility.

Discovery and probe

No fixed well-known path; a client is coded against a known agent backend endpoint that emits an AG-UI-compatible event stream over an agreed transport (SSE, WebSockets, webhooks)

POST {endpoint} — the application-defined AG-UI run endpoint (no fixed path; confirmed per-integration, e.g. via a framework's AG-UI adapter)
parse:     Response is an event stream using AG-UI's ~16 standard event types (e.g. TEXT_MESSAGE_START/CONTENT/END, RUN_ERROR, STATE_SNAPSHOT); presence of these event names confirms AG-UI compliance
on absent: No AG-UI-shaped event stream; the backend is not exposing an AG-UI-compatible interface

Not probed live: no-fixed-path. The AG-UI run endpoint is application-defined.

History

Instances

Every instance with its source is listed on the instances page.

See also

References

  1. CopilotKit's own announcement post, dated May 12, 2025, introduces AG-UI as 'an open, lightweight protocol that streams a single sequence of JSON events over standard HTTP or an optional binary channel.' — https://webflow.copilotkit.ai/blog/introducing-ag-ui-the-protocol-where-agents-meet-users (2025-05-12) VERIFIED
  2. docs.ag-ui.com/introduction (fetched 2026-09-05) describes AG-UI as an open, lightweight, event-based protocol, positions it as the 'Agent ↔ User Interaction' layer alongside MCP (Agent ↔ Tools & Data, from Anthropic) and A2A (Agent ↔ Agent, from Google), and lists 1st-party integrations from Microsoft Agent Framework, Google ADK, AWS Strands/Bedrock AgentCore, plus SDKs in Kotlin, Go, Dart, Java, Rust, Ruby, C++, .NET. — https://docs.ag-ui.com/introduction (2026-09-05) VERIFIED
  3. GitHub repo github.com/ag-ui-protocol/ag-ui carries an MIT license, 15.7k stars, 3,840+ commits, and daily commit activity as of Sep 4-5, 2026, indicating an actively maintained, multi-contributor project rather than a dormant announcement. — https://github.com/ag-ui-protocol/ag-ui (2026-09-05) VERIFIED

JSON · Markdown