MCP Apps playground
Build and preview MCP client UX. Connect to any MCP server, call a tool, and watch its interactive UI resource render live in a sandboxed iframe — the same way Claude, ChatGPT, VS Code, and other MCP hosts surface it. Perfect for iterating on the UI bundle your tool returns before shipping the server.
What is an MCP App?
A tool whose result ships an interactive UI component. The server declares _meta.ui.resourceUri on the tool descriptor pointing at a ui://… resource; the host reads that resource and renders its HTML inside a sandboxed iframe. The iframe talks back to the host over postMessage to call follow-up tools, update model context, and send messages — all without re-prompting.
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