docs/introduction/agent-ui-ecosystem.md
The agentic UI space is evolving rapidly. Here's how A2UI relates to the other major approaches.
| A2UI | MCP Apps | AG UI | |
|---|---|---|---|
| Approach | Declarative component blueprints | Pre-built HTML via ui:// URIs | High-bandwidth protocol connecting backends to frontends |
| Rendering | Native components (Angular, Flutter, Lit, etc.) | Sandboxed iframe | Developer-defined (any framework) |
| Styling | Host app controls — inherits design system | Isolated — remote server controls appearance | Developer controls — part of the host app |
| Security | Declarative data, no code execution | Sandboxed iframe isolation | Trusted code within your own app |
| Multi-agent | ✅ Across trust boundaries | ✅ Multiple MCP servers | ⚠️ Primarily single-agent |
| Cross-platform | ✅ Web, mobile, desktop, native | ⚠️ Web-focused (iframe) | ✅ Protocol is framework-agnostic |
| LLM generation | ✅ Designed for streaming output | ❌ Pre-built by server | ✅ Via A2UI integration |
| Spec | Open protocol (Apache 2.0) | MCP extension (SEP-1865) | Open source (by CopilotKit) |
MCP Apps treat UI as a resource — servers provide pre-built HTML via ui:// URIs, rendered in sandboxed iframes. The remote integration controls all content and appearance, with configuration happening through tool calling. A2UI takes a declarative UI approach — agents send component blueprints, but the host application controls styling, theming, and how those components are configured and rendered. Choose MCP Apps when the server should own the full UI experience; choose A2UI when you want dynamic, cross-platform UI that fits naturally into your app.
AG UI is a transport protocol connecting agent backends to frontends with real-time state sync. A2UI is a UI format — the payload that describes what to render. They're complementary: use AG UI as the pipe, A2UI as the content. AG UI is a project by the CopilotKit team, who also contributed the A2UI Composer. AG UI has day-zero A2UI compatibility.
ChatKit offers a tightly integrated experience within the OpenAI ecosystem. A2UI shares some design philosophy with ChatKit — both define a set of basic components and use a configurable, declarative abstraction layer. A2UI is platform-agnostic — designed for developers building their own agentic surfaces across web, mobile, and desktop, or for multi-agent systems where agents need to render UI across trust boundaries.
These approaches are complementary, not competing: