Agent UI Index Join waitlist

Which agent UI?

A neutral index of agent frontend libraries and protocols. CopilotKit, assistant-ui, ChatKit, AG-UI, A2UI, MCP Apps. with a compatibility matrix and a live demo for every pairing. No vendor docs spin.

Join the waitlist Read the matrix
Tool What it is Plays with
AG-UI Transport protocol: agent backend ↔ frontend with real-time state sync (by CopilotKit) LangChain, Mastra, PydanticAI, CrewAI; carries A2UI
A2UI Declarative JSON UI format (Apache 2.0). The agent can only request components from your trusted catalog Web & Flutter renderers; A2A and AG-UI transports
MCP Apps MCP extension (SEP-1865). Servers ship pre-built HTML via ui://, rendered in sandboxed iframes MCP hosts
CopilotKit Agent frontend SDK for chat, generative UI, shared state, human-in-the-loop React, Angular, Vue, React Native, Slack, Teams
assistant-ui Composable React primitives. Generative-UI package with a 35-component default vocabulary LangGraph data UI; consumes A2UI over AG-UI
ChatKit OpenAI's chat UI kit. Tightly integrated with the OpenAI ecosystem OpenAI agents

Sources: project docs and repos, checked Oct 2026. Full matrix + demos at launch. Click Protocols / Libraries to filter.

Why this exists

Agent backends multiply every month. The harder question for a React team is which frontend stack and protocol actually wire into them without buying a vendor’s whole worldview.

Agent UI Index keeps one matrix, one set of demos, and one changelog. Protocols and libraries sit in the same table so you can see that AG-UI is a pipe, A2UI is a payload, and MCP Apps put the server in charge of the HTML.

Independent. Built by a React developer who ships agent UIs for a living. Not affiliated with any listed project. Get launch access.

How the stack layers
UI libraries
CopilotKit assistant-ui ChatKit
UI formats and transport
A2UI MCP Apps AG-UI
Agent backends
LangGraph Mastra CrewAI PydanticAI OpenAI Agents

Live links from the matrix: assistant-ui consumes A2UI over AG-UI. AG-UI is by CopilotKit and talks to LangGraph-class backends. ChatKit sits on OpenAI Agents. MCP Apps speak to MCP hosts (not shown as a separate backend here).

What ships at launch

Compatibility matrix Which UI library works with which agent backend and protocol. Updated when the docs change.
Table
Same agent, every UI One reference agent wired into each library, side by side, so the comparison is visual not marketing copy.
Demos
Release changelog Breaking changes and new specs, tracked in one place. The feed behind the weekly email.
Email

How the pieces fit

AG-UI is the pipe. A2UI is the JSON payload your app renders. MCP Apps ship pre-built HTML. Libraries sit on top. The matrix keeps those layers distinct.

Layer mapprotocol · format · library
Pipe

AG-UI. agent backend ↔ frontend transport with real-time state sync

Payload

A2UI. declarative JSON UI; components only from your trusted catalog

Resource

MCP Apps. server-owned HTML via ui:// in sandboxed iframes

UI kits

CopilotKit · assistant-ui · ChatKit. how you actually paint the surface

What changed in agent UIsample feed

A2UI. v0.9 schema rewrite; bidirectional with AG-UI and A2A

CopilotKit: AG-UI client for React Native (generative UI, threads, HITL)

OpenUI: OUI-1 model aimed at generative UI composition

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You'll also get “What changed in agent UI”: one short email a week on new releases, spec changes and breaking changes. Unsubscribe anytime.