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AG-UI Protocol

open source / Overall score: 5.0(leading)

Open event-based protocol standardizing how an AI agent connects to a user-facing application. Agent backends emit one of about sixteen standard event types over any transport, and front ends consume them through community SDKs in eight languages.

The fourth specification on this map and the one that completes the set its own README describes: "MCP gives agents tools / A2A allows agents to communicate with other agents / AG-UI brings agents into user-facing applications". Born from CopilotKit's partnership with LangChain and CrewAI, and its MIT copyright line names no holder.

Openness

5 high confidence

5.0

license: MIT(OSI)
source: public(the specification, the reference HTTP implementation and the SDKs)
self-host: yes(the protocol and its SDKs are the product)
core features withheld: no — no vendor tier

MIT covers the specification, the reference implementation and the SDK matrix, and the license file is the plain MIT text with no added terms.

https://api.github.com/repos/ag-ui-protocol/ag-ui recorded 2026-09-17
Repository metadata: spdx_id MIT, 15,930 stars, not archived, not a fork, last pushed 2026-09-17, description "AG-UI: the Agent-User Interaction Protocol. Bring Agents into Frontend Applications."
https://raw.githubusercontent.com/ag-ui-protocol/ag-ui/main/LICENSE recorded 2026-09-17
The LICENSE body: the verbatim MIT text. Its copyright line reads "Copyright (c) 2025" and names no holder.

Adoption

5 high confidence

5.0

Adoption is measured as combined downloads of the `ag-ui-protocol` PyPI package and the `@ag-ui/core` npm package, the two channels the protocol ships SDKs through. Both count toward the same product because AG-UI distributes as separate Python and JavaScript packages rather than one channel.

https://api.npmjs.org/downloads/point/last-month/@ag-ui/core recorded 2026-09-17
npm downloads point API: 7,171,054 downloads for `@ag-ui/core` over 2026-08-13 to 2026-09-11.
https://pypistats.org/api/packages/ag-ui-protocol/recent recorded 2026-09-17
last_month = 6,655,537 downloads for `ag-ui-protocol` (last_week 1,551,841, last_day 280,818).

Capability

not assessed

AG-UI is a specification rather than an implementation of one, so there is nothing to measure it against — the same reason the Model Context Protocol, the Agent2Agent Protocol and the Agent Client Protocol are left unscored. It is also transport-agnostic, working over any event transport such as SSE, WebSockets or webhooks, so there is no fixed transport surface to measure either.

https://raw.githubusercontent.com/ag-ui-protocol/ag-ui/main/README.md recorded 2026-09-17
The README: "AG-UI is an open, lightweight, event-based protocol that standardizes how AI agents connect to user-facing applications", with agent backends emitting "events compatible with one of AG-UI's ~16 standard event types" and the protocol working with "any event transport (SSE, WebSockets, webhooks, etc.)". It positions itself alongside MCP and A2A rather than as an implementation of either.

Verified 2026-09-17