@modelcontextprotocol/ext-apps - v0.0.1

@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.

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/simple-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

This repo is in flux and isn't published to npm yet. When it is, it will use the @modelcontextprotocol/ext-apps package.

In the meantime you can depend on the SDK library in a Node.js project by installing it with its git URL:

npm install -S git+https://github.com/modelcontextprotocol/ext-apps.git

Your package.json will then look like:

{
  "dependencies": {
    "@modelcontextprotocol/ext-apps": "git+https://github.com/modelcontextprotocol/ext-apps.git"
  }
}

Note

The build tools (esbuild, tsx, typescript) are in dependencies rather than devDependencies. This is intentional: it allows the prepare script to run when the package is installed from git, since npm doesn't install devDependencies for git dependencies.

Once the package is published to npm with pre-built dist/, these can be moved back to devDependencies.

Examples

examples/simple-server — Example MCP server with tools that return UI Apps
examples/simple-host — Bare-bones example of hosting MCP Apps

To run the examples end-to-end:

npm i
npm start

Then open http://localhost:8080/