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The Model Context Protocol ecosystem, verified

Current spec 2026-07-28

MCP Apps

ecosystem

MCP Apps - The extension that lets a tool return an interactive HTML interface rendered inside the chat: the tool description points at a ui:// resource, the host renders it in a sandboxed iframe, and app and host speak a JSON-RPC dialect over postMessage with bidirectional data flow.

MCP Apps extend tools beyond text: a tool's description carries _meta.ui.resourceUri pointing at a ui:// resource, the host fetches that HTML and renders it in a sandboxed iframe inside the conversation, and the app talks to the host over a JSON-RPC dialect on postMessage. The app can call the server's tools through the host and receive fresh data pushed back, while the sandbox keeps it away from the host page, cookies, and storage.

Client support at the time of verification included Claude and Claude Desktop, VS Code GitHub Copilot, Microsoft 365 Copilot, Goose, Postman, MCPJam, and Archestra.AI. The Apps Working Group charter, published 2026-08-12, governs the extension's evolution.

Related concepts

Sources and verification

Last verified · confidence 1.00.

  1. Official MCP Apps overview - "MCP Apps let servers return interactive HTML interfaces (data visualizations, forms, dashboards) that render directly in the chat"; the tool description carries _meta.ui.resourceUri pointing at a ui:// resource; hosts render in a sandboxed iframe with postMessage communication; supported by Claude, Claude Desktop, VS Code GitHub Copilot, Microsoft 365 Copilot, Goose, Postman, MCPJam, and Archestra.AI - accessed

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