No universal winner—only matched responsibilities.
Use this matrix to begin a decision, then verify primary sources and security boundaries. Scroll horizontally on small screens.
| Technology | Layer | Kind | Maturity | Choose when | Avoid when | Composes with |
|---|---|---|---|---|---|---|
| AG-UIprimary source | interaction | protocol | active | You need a bidirectional connection between an agent backend and a product-owned frontend. | You only need a UI component schema and already have a complete transport and run lifecycle. | a2ui + openui + json-render + copilotkit + a2a + mcp |
| A2UIprimary source | declarative | specification | public preview | The same agent-generated UI intent must render across web, Flutter, or other native clients. | You need a stable version-one wire contract today or only target one tightly controlled React application. | ag-ui + copilotkit + a2a |
| OpenUIprimary source | declarative | framework | active | You want a React-oriented end-to-end framework with compact streamed UI output and ready-made component libraries. | Your primary requirement is framework-neutral cross-platform interoperability rather than React runtime ergonomics. | ag-ui + copilotkit |
| json-renderprimary source | declarative | framework | active | You already think in component catalogs and want schema-constrained JSON with progressive rendering. | You need an agent run transport or prefer a compact non-JSON language optimized for minimal token use. | ag-ui + mcp-apps |
| Open-JSON-UIecosystem source | declarative | specification | emerging | You are evaluating the CopilotKit Generative UI examples that explicitly describe Open-JSON-UI payloads. | Procurement, compliance, or long-term interoperability requires a first-party published specification and independent conformance suite. | ag-ui + copilotkit |
| MCP Appsprimary source | extension | stable | Your interface must render inside a compatible AI chat host and call server tools through the host. | You own a conventional web application and do not benefit from host embedding, context preservation, or MCP tool access. | json-render + mcp | |
| CopilotKitprimary source | implementation | platform | active | You want production-oriented React components and runtime integrations around AG-UI rather than implementing every client primitive yourself. | You only need the vendor-neutral protocol types or are building a non-React client with a deliberately minimal dependency surface. | ag-ui + a2ui + mcp-apps + open-json-ui |
Open-JSON-UI is currently described from CopilotKit ecosystem documentation; no independent first-party OpenAI specification repository has been verified.