@modelcontextprotocol/ext-apps

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

Specification

Version	Status	Link
2026-01-26	Stable	specification/2026-01-26/apps.mdx
draft	Development	specification/draft/apps.mdx

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.

Why MCP Apps?

MCP tools return text and structured data. That works for many cases, but not when you need an interactive UI, like a chart, form, or video player.

MCP Apps provide a standardized way to deliver interactive UIs from MCP servers. Your UI renders inline in the conversation, in context, in any compliant host.

How It Works

MCP Apps extend the Model Context Protocol by letting tools declare UI resources:

1. Tool definition — Your tool declares a ui:// resource containing its HTML interface
2. Tool call — The LLM calls the tool on your server
3. Host renders — The host fetches the resource and displays it in a sandboxed iframe
4. Bidirectional communication — The host passes tool data to the UI via notifications, and the UI can call other tools through the host

Using the SDK

This SDK serves two audiences:

For 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

For 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).

The MCP-UI client SDK offers a fully-featured MCP Apps framework used by a few hosts. Clients may choose to use it or roll their own implementation.

Installation

npm install -S @modelcontextprotocol/ext-apps

Install Agent Skills

This repository provides two Agent Skills for building MCP Apps. You can install the skills as a Claude Code plugin:

/plugin marketplace add modelcontextprotocol/ext-apps
/plugin install mcp-apps@modelcontextprotocol-ext-apps

For more information, including instructions for installing the skills in your favorite AI coding agent, see the agent skills guide.

Examples

The examples/ directory contains demo apps showcasing real-world use cases.

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)	Say Demo

Starter Templates

	The same app built with different frameworks — pick your favorite! React · Vue · Svelte · Preact · Solid · Vanilla JS

Running the Examples

With basic-host

To run all examples locally using basic-host (the reference host implementation included in this repo):

git clone https://github.com/modelcontextprotocol/ext-apps.git
cd ext-apps
npm install
npm start

Then open http://localhost:8080/.

With MCP Clients

To use these examples with MCP clients that support the stdio transport (such as Claude Desktop or VS Code), add this MCP server configuration to your client's settings:

MCP client configuration for all examples (using stdio)

{
  "mcpServers": {
    "basic-react": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-basic-react",
        "--stdio"
      ]
    },
    "basic-vanillajs": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-basic-vanillajs",
        "--stdio"
      ]
    },
    "basic-vue": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-basic-vue",
        "--stdio"
      ]
    },
    "basic-svelte": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-basic-svelte",
        "--stdio"
      ]
    },
    "basic-preact": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-basic-preact",
        "--stdio"
      ]
    },
    "basic-solid": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-basic-solid",
        "--stdio"
      ]
    },
    "budget-allocator": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-budget-allocator",
        "--stdio"
      ]
    },
    "cohort-heatmap": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-cohort-heatmap",
        "--stdio"
      ]
    },
    "customer-segmentation": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-customer-segmentation",
        "--stdio"
      ]
    },
    "map": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-map",
        "--stdio"
      ]
    },
    "pdf": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-pdf",
        "--stdio"
      ]
    },
    "scenario-modeler": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-scenario-modeler",
        "--stdio"
      ]
    },
    "shadertoy": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-shadertoy",
        "--stdio"
      ]
    },
    "sheet-music": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-sheet-music",
        "--stdio"
      ]
    },
    "system-monitor": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-system-monitor",
        "--stdio"
      ]
    },
    "threejs": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-threejs",
        "--stdio"
      ]
    },
    "transcript": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-transcript",
        "--stdio"
      ]
    },
    "video-resource": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-video-resource",
        "--stdio"
      ]
    },
    "wiki-explorer": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-wiki-explorer",
        "--stdio"
      ]
    },
    "qr": {
      "command": "uv",
      "args": [
        "run",
        "/path/to/ext-apps/examples/qr-server/server.py",
        "--stdio"
      ]
    },
    "say": {
      "command": "uv",
      "args": [
        "run",
        "--default-index",
        "https://pypi.org/simple",
        "https://raw.githubusercontent.com/modelcontextprotocol/ext-apps/refs/heads/main/examples/say-server/server.py",
        "--stdio"
      ]
    }
  }
}

Note

The qr server requires cloning the repository first. See qr-server README for details.

Local Development

To test local modifications with MCP clients, first clone and install the repository:

git clone https://github.com/modelcontextprotocol/ext-apps.git
cd ext-apps
npm install

Then configure your MCP client to build and run the local server. Replace ~/code/ext-apps with your actual clone path:

MCP client configuration for local development (all examples)

{
  "mcpServers": {
    "basic-react": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/basic-server-react && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "basic-vanillajs": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/basic-server-vanillajs && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "basic-vue": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/basic-server-vue && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "basic-svelte": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/basic-server-svelte && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "basic-preact": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/basic-server-preact && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "basic-solid": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/basic-server-solid && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "budget-allocator": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/budget-allocator-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "cohort-heatmap": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/cohort-heatmap-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "customer-segmentation": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/customer-segmentation-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "map": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/map-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "pdf": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/pdf-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "scenario-modeler": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/scenario-modeler-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "shadertoy": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/shadertoy-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "sheet-music": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/sheet-music-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "system-monitor": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/system-monitor-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "threejs": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/threejs-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "transcript": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/transcript-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "video-resource": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/video-resource-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "wiki-explorer": {
      "command": "bash",
      "args": [
        "-c",
        "cd ~/code/ext-apps/examples/wiki-explorer-server && npm run build >&2 && node dist/index.js --stdio"
      ]
    },
    "qr": {
      "command": "bash",
      "args": [
        "-c",
        "uv run ~/code/ext-apps/examples/qr-server/server.py --stdio"
      ]
    },
    "say": {
      "command": "bash",
      "args": [
        "-c",
        "uv run --index https://pypi.org/simple ~/code/ext-apps/examples/say-server/server.py --stdio"
      ]
    }
  }
}

This configuration rebuilds each server on launch, ensuring your local changes are picked up.

Resources

• Quickstart Guide
• API Documentation
• Specification (2026-01-26) (Draft)
• SEP-1865 Discussion