MCP Apps

MCP Apps is the first official MCP extension (spec 2026-01-26, co-authored by Anthropic and OpenAI). It enables interactive HTML UIs rendered in sandboxed iframes inside MCP hosts. Extension ID: io.modelcontextprotocol/ui. npm package: @modelcontextprotocol/ext-apps.

MCP Apps bridge the gap between LLM tool calls and rich visual interfaces — the model sees text, users see interactive UIs.

Quick Start

The fastest path is the official create-mcp-app skill from the ext-apps repo:

npx skills add modelcontextprotocol/ext-apps --skill create-mcp-app

Then ask the agent: "Create an MCP App that displays a color picker." For manual setup, see references/build-guide.md.

Architecture

Three layers: