modelcontextprotocol/ext-apps
Watch
1
0
Fork
You've already forked ext-apps
 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions
ext-apps/README.md
Olivier Chafik 6d083cd69f Address review: MCPB build, guard the SDK's own handlers, doc fixes 
- pdf-server build-mcpb.mjs packs the ext-apps build from this checkout
  into the staging dir instead of asking the registry for ^2.0.0, which
  is not published yet; CI's "Build MCPB bundle" step failed on ETARGET.
- Claim notifications/cancelled and notifications/progress in the
  MethodRegistry right after super() so a direct setNotificationHandler
  cannot silently replace the base Protocol's own handlers.
- Migration guide and add-app-to-server skill: custom methods use the
  three-argument setRequestHandler("m", { params }, handler) form (the
  two-argument form is only for spec methods); zod schemas live in
  @modelcontextprotocol/core, not client/server; it is
  toolInfo.tool.outputSchema that loosened in schema.json, and the
  recursive JSON-value def is nested under three definitions; core is a
  required peer that client already depends on.
- app-bridge.ts: fix "forthe"/"forresult" typos in @see links, update
  three JSDoc examples to the method-string setNotificationHandler form,
  move the UntypedHandlerSetter type below the import block (same in
  app.ts).
- wire-compat.test.ts: say the fixtures are 1.x-shaped, not captures.
2026-09-08 13:59:09 +01:00

284 lines
18 KiB
Markdown
Raw Blame History

<!-- LOGO -->
<div align="center">
<picture>
<source media="(prefers-color-scheme: dark)" srcset="media/mcp-white.svg">
<source media="(prefers-color-scheme: light)" srcset="media/mcp.svg">
<img src="media/mcp.svg" alt="MCP Apps" width="128">
</picture>
<h1>MCP Apps</h1>
<p>
Build interactive UIs for MCP tools — charts, forms, dashboards — that render inline in Claude, ChatGPT and any other compliant chat client.
<br /><br />
<a href="#why-mcp-apps">Why</a>
·
<a href="https://apps.extensions.modelcontextprotocol.io/api/documents/Quickstart.html">Quickstart</a>
·
<a href="https://apps.extensions.modelcontextprotocol.io/api/">API Docs</a>
·
<a href="https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/2026-01-26/apps.mdx">Spec</a>
·
<a href="CONTRIBUTING.md">Contributing</a>
</p>
</div>
<p align="center">
<a href="https://github.com/modelcontextprotocol/ext-apps/actions/workflows/ci.yml"><img src="https://github.com/modelcontextprotocol/ext-apps/actions/workflows/ci.yml/badge.svg" alt="CI"></a>
<a href="LICENSE"><img src="https://img.shields.io/badge/license-Apache%202.0-blue" alt="License: Apache 2.0"></a>
<a href="https://www.npmjs.com/package/@modelcontextprotocol/ext-apps"><img src="https://img.shields.io/npm/v/@modelcontextprotocol/ext-apps.svg" alt="npm version"></a>
<a href="https://www.npmjs.com/package/@modelcontextprotocol/ext-apps"><img src="https://img.shields.io/npm/dm/@modelcontextprotocol/ext-apps.svg" alt="npm downloads"></a>
<a href="https://github.com/modelcontextprotocol/ext-apps"><img src="https://img.shields.io/github/stars/modelcontextprotocol/ext-apps" alt="GitHub stars"></a>
<a href="https://apps.extensions.modelcontextprotocol.io/api/"><img src="https://img.shields.io/badge/docs-API%20Reference-blue" alt="API Documentation"></a>
</p>
<p align="center">
<img src="media/excalidraw.gif" alt="MCP Apps demo" width="600">
<br><em>Excalidraw built with MCP Apps, running in Claude</em>
</p>
## Table of Contents
- [Build with Agent Skills](#build-with-agent-skills)
- [Supported Clients](#supported-clients)
- [Why MCP Apps?](#why-mcp-apps)
- [How It Works](#how-it-works)
- [Getting Started](#getting-started)
- [Using the SDK](#using-the-sdk)
- [Examples](#examples)
- [Specification](#specification)
- [Resources](#resources)
- [Contributing](#contributing)
## Build with Agent Skills
The fastest way to build an MCP App is to let your AI coding agent do it. This
repo ships four [Agent Skills](https://agentskills.io/) — install them once,
then just ask:
| Skill | What it does | Try it |
| --------------------------------------------------------------------------- | ----------------------------------------------------------- | ------------------------------------- |
| [`create-mcp-app`](./plugins/mcp-apps/skills/create-mcp-app/SKILL.md) | Scaffolds a new MCP App with an interactive UI from scratch | _"Create an MCP App"_ |
| [`migrate-oai-app`](./plugins/mcp-apps/skills/migrate-oai-app/SKILL.md) | Converts an existing OpenAI App to use MCP Apps | _"Migrate from OpenAI Apps SDK"_ |
| [`add-app-to-server`](./plugins/mcp-apps/skills/add-app-to-server/SKILL.md) | Adds interactive UI to an existing MCP server's tools | _"Add UI to my MCP server"_ |
| [`convert-web-app`](./plugins/mcp-apps/skills/convert-web-app/SKILL.md) | Turns an existing web app into a hybrid web + MCP App | _"Add MCP App support to my web app"_ |
### Install the Skills
**Claude Code** — install via the plugin marketplace:
```
/plugin marketplace add modelcontextprotocol/ext-apps
/plugin install mcp-apps@modelcontextprotocol-ext-apps
```
**Other agents** — any AI coding agent that supports
[Agent Skills](https://agentskills.io/) can use these skills. See the
[agent skills guide](./docs/agent-skills.md) for manual installation
instructions.
Once installed, verify by asking your agent _"What skills do you have?"_ — you
should see `create-mcp-app`, `migrate-oai-app`, `add-app-to-server`, and
`convert-web-app` in the list. Then just ask it to create or migrate an app and
it will guide you through the rest.
## Supported Clients
<p align="center">
<a href="https://developers.openai.com/apps-sdk/mcp-apps-in-chatgpt/"><img src="https://img.shields.io/badge/ChatGPT-docs-74aa9c?logo=openai&logoColor=white" alt="ChatGPT"></a>
<a href="https://claude.com/docs/connectors/building/mcp-apps/getting-started"><img src="https://img.shields.io/badge/Claude-docs-d97706?logo=claude&logoColor=white" alt="Claude"></a>
<a href="https://code.visualstudio.com/blogs/2026/01/26/mcp-apps-support"><img src="https://img.shields.io/badge/VS_Code-docs-007ACC?logo=visualstudiocode&logoColor=white" alt="VS Code"></a>
<a href="https://block.github.io/goose/docs/tutorials/building-mcp-apps/"><img src="https://img.shields.io/badge/Goose-docs-000000?logo=goose&logoColor=white" alt="Goose"></a>
<a href="https://learning.postman.com/docs/postman-ai/mcp-requests/interact"><img src="https://img.shields.io/badge/Postman-docs-FF6C37?logo=postman&logoColor=white" alt="Postman"></a>
<a href="https://www.mcpjam.com/blog/mcp-apps-example"><img src="https://img.shields.io/badge/MCPJam-docs-8B5CF6" alt="MCPJam"></a>
<a href="https://manufact.com/inspector"><img src="https://img.shields.io/badge/mcp--use-inspector-E5F3FD" alt="mcp-use"></a>
<a href="https://docs.alpic.ai/distribution/playground"><img src="https://img.shields.io/badge/Alpic-playground-E90060?logo=data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAGQAAABkCAMAAABHPGVmAAAAKlBMVEUKDhz%2F%2F%2F%2BjpaogJDFBRE%2Fw8PHHyMvh4eNmaHF1d4CUlpuFho2ztLhWWWP5YkbJAAAACXBIWXMAAAsTAAALEwEAmpwYAAAB1klEQVR42u2Y0ZKDIAxFBQQF8f9%2FdyW7dhAu7U7Iy87mzvShGfXU3CTGLotKpVKpVCqV6h%2FI2VuxfF3tUwcdVEccA2LNS%2BWCq2mUykG%2BCtg5iNmv76mllOApCPHrFQgNxJf8HHIQs10XdFtDKcEKPQ0x4brg6htKWGr0PIR8jq0tj4oQgJiIzD8rtATErMAWMj%2FxIYcBPjuPgoENcW3Jks%2BdLeXS32jLmise%2BZxQ8GRD%2BkkCbSlByi0Pgm3p0P6nJ1meXJ%2F8K1tKo7qUOFM4wdxEMMS4iSp9sqFJQrZ4hOZBTEa5gbaQ%2BTwI%2FcCu8TOq482xIWZkSx8MfAi0xcOEJTZkULKohXjm29epGU2SIGK%2BfT9J%2Bjre%2BRBYsiUYBSHkaEI2B0EInRx%2BkbApiB89EaMgBNdx7u5vDoJH79ne3yQElqxvEzYLKY%2Bl81PCZiFUsvlDwqYhw80uSkJg4z8Ttsss3OltwgQgMGGPlpSAwITVM0wCgius6iARCGzJcn%2BHJCSMXraCIATPsPW2SggCh364a1sIgveUew%2BTgtBGsuE9zDspyLBZ3M5aVCOCUDFlqXUbrm8j7%2FnvJ2B9G3kf%2BZBlt0iu%2Fr%2BNxHqRU6lUKpVKpVL9UX0BOrAPfcbTY8UAAAAASUVORK5CYII%3D" alt="Alpic Playground"></a>
</p>
> [!NOTE]
> MCP Apps is an extension to the
> [core MCP specification](https://modelcontextprotocol.io/specification). Host
> support varies — see the
> [clients page](https://modelcontextprotocol.io/clients) for the full list.
## 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, design canvas 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
## Getting Started
Requires Node.js 20+. The base MCP SDK packages are `^2.0.0` peers of
`ext-apps` (`@modelcontextprotocol/core` is a required peer that `client` already depends on, so npm installs it for you).
For a View or host:
```bash
npm install -S @modelcontextprotocol/ext-apps \
@modelcontextprotocol/client@^2.0.0 \
zod@^4.2.0
```
For an MCP server, add the server package (and, for HTTP transports, the Node
and Express adapters):
```bash
npm install -S @modelcontextprotocol/ext-apps \
@modelcontextprotocol/client@^2.0.0 \
@modelcontextprotocol/server@^2.0.0 \
@modelcontextprotocol/node@^2.0.0 \
@modelcontextprotocol/express@^2.0.0 \
zod@^4.2.0
```
The wire protocol is unchanged between `ext-apps` 1.x and 2.x: a 2.x View works
in a 1.x host and a 2.x host renders 1.x Views. See the
[migration guide](https://apps.extensions.modelcontextprotocol.io/api/documents/migrate-to-v2.html)
when upgrading from 1.x.
**New here?** Start with the
[Quickstart Guide](https://apps.extensions.modelcontextprotocol.io/api/documents/Quickstart.html)
to build your first MCP App.
## Using the SDK
The SDK serves three roles: app developers building interactive Views, host
developers embedding those Views, and MCP server authors registering tools with
UI metadata.
| Package | Purpose | Docs |
| ------------------------------------------- | --------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------- |
| `@modelcontextprotocol/ext-apps` | Build interactive Views (App class, PostMessageTransport) | [API Docs →](https://apps.extensions.modelcontextprotocol.io/api/modules/app.html) |
| `@modelcontextprotocol/ext-apps/react` | React hooks for Views (useApp, useHostStyles, etc.) | [API Docs →](https://apps.extensions.modelcontextprotocol.io/api/modules/_modelcontextprotocol_ext-apps_react.html) |
| `@modelcontextprotocol/ext-apps/app-bridge` | Embed and communicate with Views in your chat client | [API Docs →](https://apps.extensions.modelcontextprotocol.io/api/modules/app-bridge.html) |
| `@modelcontextprotocol/ext-apps/server` | Register tools and resources on your MCP server | [API Docs →](https://apps.extensions.modelcontextprotocol.io/api/modules/server-helpers.html) |
There's no _supported_ host implementation in this repo (beyond the
[examples/basic-host](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-host)
example).
The [MCP-UI](https://github.com/idosal/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.
## Examples
The
[`examples/`](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples)
directory contains demo apps showcasing real-world use cases.
<!-- prettier-ignore-start -->
| | | |
|:---:|:---:|:---:|
| [![Map](examples/map-server/grid-cell.png "Interactive 3D globe viewer using CesiumJS")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/map-server) | [![Three.js](examples/threejs-server/grid-cell.png "Interactive 3D scene renderer")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/threejs-server) | [![ShaderToy](examples/shadertoy-server/grid-cell.png "Real-time GLSL shader renderer")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/shadertoy-server) |
| [**Map**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/map-server) | [**Three.js**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/threejs-server) | [**ShaderToy**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/shadertoy-server) |
| [![Sheet Music](examples/sheet-music-server/grid-cell.png "ABC notation to sheet music")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/sheet-music-server) | [![Wiki Explorer](examples/wiki-explorer-server/grid-cell.png "Wikipedia link graph visualization")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/wiki-explorer-server) | [![Cohort Heatmap](examples/cohort-heatmap-server/grid-cell.png "Customer retention heatmap")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/cohort-heatmap-server) |
| [**Sheet Music**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/sheet-music-server) | [**Wiki Explorer**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/wiki-explorer-server) | [**Cohort Heatmap**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/cohort-heatmap-server) |
| [![Scenario Modeler](examples/scenario-modeler-server/grid-cell.png "SaaS business projections")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/scenario-modeler-server) | [![Budget Allocator](examples/budget-allocator-server/grid-cell.png "Interactive budget allocation")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/budget-allocator-server) | [![Customer Segmentation](examples/customer-segmentation-server/grid-cell.png "Scatter chart with clustering")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/customer-segmentation-server) |
| [**Scenario Modeler**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/scenario-modeler-server) | [**Budget Allocator**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/budget-allocator-server) | [**Customer Segmentation**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/customer-segmentation-server) |
| [![System Monitor](examples/system-monitor-server/grid-cell.png "Real-time OS metrics")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/system-monitor-server) | [![Transcript](examples/transcript-server/grid-cell.png "Live speech transcription")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/transcript-server) | [![Video Resource](examples/video-resource-server/grid-cell.png "Binary video via MCP resources")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/video-resource-server) |
| [**System Monitor**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/system-monitor-server) | [**Transcript**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/transcript-server) | [**Video Resource**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/video-resource-server) |
| [![PDF Server](examples/pdf-server/grid-cell.png "Interactive PDF viewer with chunked loading")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/pdf-server) | [![QR Code](examples/qr-server/grid-cell.png "QR code generator")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/qr-server) | [![Say Demo](examples/say-server/grid-cell.png "Text-to-speech demo")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/say-server) |
| [**PDF Server**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/pdf-server) | [**QR Code (Python)**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/qr-server) | [**Say Demo**](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/say-server) |
### Starter Templates
| | |
|:---:|:---|
| [![Basic](examples/basic-server-react/grid-cell.png "Starter template")](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-server-react) | The same app built with different frameworks — pick your favorite!<br><br>[React](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-server-react) · [Vue](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-server-vue) · [Svelte](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-server-svelte) · [Preact](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-server-preact) · [Solid](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-server-solid) · [Vanilla JS](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-server-vanillajs) |
<!-- prettier-ignore-end -->
### Running the Examples
#### With basic-host
To run all examples locally using
[basic-host](https://github.com/modelcontextprotocol/ext-apps/tree/main/examples/basic-host)
(the reference host implementation included in this repo):
```bash
git clone https://github.com/modelcontextprotocol/ext-apps.git
cd ext-apps
npm install
npm start
```
Then open http://localhost:8080/.
#### With MCP Clients
Every Node.js example is published as `@modelcontextprotocol/server-<name>`. To
add one to an MCP client that supports stdio (Claude Desktop, VS Code, etc.),
use this pattern:
```json
{
"mcpServers": {
"<name>": {
"command": "npx",
"args": ["-y", "@modelcontextprotocol/server-<name>", "--stdio"]
}
}
}
```
For example, to add the map server: `@modelcontextprotocol/server-map`. The
Python examples (`qr-server`, `say-server`) use `uv run` instead — see their
READMEs for details.
#### Local Development
To test local modifications with an MCP client, clone the repo, install, then
point your client at a local build:
```json
{
"mcpServers": {
"<name>": {
"command": "bash",
"args": [
"-c",
"cd ~/code/ext-apps/examples/<name>-server && npm run build >&2 && node dist/index.js --stdio"
]
}
}
}
```
## Specification
<div align="center">
| Version | Status | Link |
| -------------- | ----------- | --------------------------------------------------------------------------------------------------------------------------------- |
| **2026-01-26** | Stable | [specification/2026-01-26/apps.mdx](https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/2026-01-26/apps.mdx) |
| **draft** | Development | [specification/draft/apps.mdx](https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/draft/apps.mdx) |
</div>
## Resources
- [Quickstart Guide](https://apps.extensions.modelcontextprotocol.io/api/documents/Quickstart.html)
- [API Documentation](https://apps.extensions.modelcontextprotocol.io/api/)
- [Specification (2026-01-26)](https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/2026-01-26/apps.mdx)
([Draft](https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/draft/apps.mdx))
- [SEP-1865 Discussion](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/1865)
## Contributing
Contributions are welcome! Please read [CONTRIBUTING.md](CONTRIBUTING.md) for
guidelines on how to get started, submit pull requests, and report issues.
Reference in a new issue View git blame Copy permalink