Return interactive HTML from MCP tools — MCP Apps renders live UI inside the chat
Model Context Protocol Blog·high signal
MCP Apps (the first official MCP extension) lets a tool return a UI resource via the ui:// scheme and a _meta.ui.resourceUri field; the host fetches the bundled HTML/JS and renders it in a sandboxed iframe with bidirectional JSON-RPC over postMessage. Inside the iframe you get callServerTool, openLink, downloadFile, and requestDisplayMode (inline/fullscreen/PiP), so forms, dashboards, and multi-step approvals run in-conversation instead of as text. It already runs in ChatGPT, Claude web/desktop, VS Code (Copilot), and Goose.