MCP Apps - Bringing UI Capabilities To MCP Clients | Model Context Protocol Blog

The architecture of MCP Apps relies on two key MCP primitives:

Tools with UI metadata: Tools include a _meta.ui.resourceUri field pointing to a UI resource UI Resources: Server-side resources served via the ui:// scheme containing bundled HTML/JavaScript // Tool with UI metadata { name: "visualize_data", description: "Visualize data as an interactive chart", inputSchema: { /* ... */ }, _meta: { ui: { resourceUri: "ui://charts/interactive" } } } The host fetches the resource, renders it in a sandboxed iframe, and enables bidirectional communication via JSON-RPC over postMessage.