Skip to main content
New in version 3.0.0 MCP Apps let your tools return interactive UIs — rendered in a sandboxed iframe right inside the host client’s conversation. Instead of returning plain text or JSON, a tool can show a chart, a form, an image viewer, or anything you can build with HTML and JavaScript. FastMCP implements the MCP Apps extension, so you can start building apps today. FastMCP 3.1 will introduce a full Python-native app framework that makes building rich UIs dramatically simpler — no HTML or JavaScript required.

​
What’s Available Today

FastMCP provides typed models and helpers for working with the MCP Apps extension directly:
  • AppConfig to link tools to UI resources and control visibility
  • ui:// resources that automatically serve HTML with the correct MIME type
  • ResourceCSP and ResourcePermissions for security and sandboxing
This is the low-level API — you write the HTML yourself and wire up communication with the host via the @modelcontextprotocol/ext-apps JavaScript SDK. It gives you full control over the UI.

​
What’s Coming in 3.1

FastMCP 3.1 will ship a Python-native app framework that lets you build interactive UIs entirely in Python. Define layouts, handle events, and manage state without writing any HTML or JavaScript — FastMCP generates the app for you. Stay tuned. In the meantime, the low-level API is ready to use.