@modelcontextprotocol/ext-apps - v0.4.1

@modelcontextprotocol/ext-apps

This repo contains the SDK and specification for MCP Apps Extension (SEP-1865).

MCP Apps are a proposed standard inspired by MCP-UI and OpenAI's Apps SDK to allow MCP Servers to display interactive UI elements in conversational MCP clients / chatbots.

How It Works

MCP Apps extend the Model Context Protocol to let servers deliver interactive UIs to MCP hosts. Here's how it works:

Tool call — The LLM calls a tool on your server
UI Resource — The tool's definition links to a predeclared ui:// resource containing its HTML interface
Host renders — The host fetches the resource and displays it in a sandboxed iframe
Bidirectional communication — The host passes tool data to the UI via notifications, and the UI can call other tools through the host

This enables dashboards, forms, visualizations, and other rich experiences inside chat interfaces.

Overview

This SDK serves two audiences:

App Developers

Build interactive UIs that run inside MCP-enabled chat clients.

SDK for Apps: @modelcontextprotocol/ext-apps — API Docs
React hooks: @modelcontextprotocol/ext-apps/react — API Docs

Host Developers

Embed and communicate with MCP Apps in your chat application.

SDK for Hosts: @modelcontextprotocol/ext-apps/app-bridge — API Docs

There's no supported host implementation in this repo (beyond the examples/basic-host example).

We have contributed a tentative implementation of hosting / iframing / sandboxing logic to the MCP-UI repository, and expect OSS clients may use it, while other clients might roll their own hosting logic.

Installation

npm install -S @modelcontextprotocol/ext-apps

Or edit your package.json manually:

{
  "dependencies": {
    "@modelcontextprotocol/ext-apps": "^0.0.1"
  }
}

Examples



Map	Three.js	ShaderToy

Sheet Music	Wiki Explorer	Cohort Heatmap

Scenario Modeler	Budget Allocator	Customer Segmentation

System Monitor	Transcript	Video Resource

PDF Server	QR Code (Python)