Enrich an existing MCP server's tools with interactive UIs using the MCP Apps SDK (@modelcontextprotocol/ext-apps).
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Before installing skills in Cursor, ensure your development environment meets these requirements:
node --versionadd-app-to-serverExecute the skills CLI command in your project's root directory to begin installation:
Fetches add-app-to-server from modelcontextprotocol/ext-apps and configures it for Cursor.
The CLI shows a list of agents. Use arrow keys and space to select Cursor:
Confirm successful installation by checking the skill directory location:
Restart Cursor to activate add-app-to-server. Access via /add-app-to-server in your agent's command palette.
We perform automated surface-level scans (Gen AI Scanner, Socket, Snyk) during installation. These checks detect common vulnerabilities but do not guarantee complete security. Always review skill source code and verify the publisher's reputation before production use.
Skills execute code in your environment. Always review source, verify the publisher, and test in isolation before production.
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Enrich an existing MCP server's tools with interactive UIs using the MCP Apps SDK (@modelcontextprotocol/ext-apps).
Existing tools get paired with HTML resources that render inline in the host's conversation. The tool continues to work for text-only clients — UI is an enhancement, not a replacement. Each tool that benefits from UI gets linked to a resource via _meta.ui.resourceUri, and the host renders that resource in a sandboxed iframe when the tool is called.
Clone the SDK repository for working examples and API documentation:
git clone --branch "v$(npm view @modelcontextprotocol/ext-apps version)" --depth 1 https://github.com/modelcontextprotocol/ext-apps.git /tmp/mcp-ext-apps
Read JSDoc documentation directly from /tmp/mcp-ext-apps/src/:
| File | Contents |
|---|---|
src/app.ts |
App class, handlers (ontoolinput, ontoolresult, onhostcontextchanged, onteardown), lifecycle |
src/server/index.ts |
registerAppTool, registerAppResource, getUiCapability, tool visibility options |
src/spec.types.ts |
All type definitions: McpUiHostContext, CSS variable keys, display modes |
src/styles.ts |
applyDocumentTheme, applyHostStyleVariables, applyHostFonts |
src/react/useApp.tsx |
useApp hook for React apps |
src/react/useHostStyles.ts |
useHostStyles, useHostStyleVariables, useHostFonts hooks |
These examples demonstrate servers with both App-enhanced and plain tools — the exact pattern you're adding:
| Example | Pattern |
|---|---|
examples/map-server/ |
show-map (App tool) + geocode (plain tool) |
examples/pdf-server/ |
display_pdf (App tool) + list_pdfs (plain tool) + read_pdf_bytes (app-only tool) |
examples/system-monitor-server/ |
get-system-info (App tool) + poll-system-stats (app-only polling tool) |
Learn and adapt from /tmp/mcp-ext-apps/examples/basic-server-{framework}/:
| Template | Key Files |
|---|---|
basic-server-vanillajs/ |
server.ts, src/mcp-app.ts, mcp-app.html |
basic-server-react/ |
server.ts, src/mcp-app.tsx (uses useApp hook) |
basic-server-vue/ |
server.ts, src/App.vue |
basic-server-svelte/ |
server.ts, src/App.svelte |
basic-server-preact/ |
server.ts, src/mcp-app.tsx |
basic-server-solid/ |
server.ts, src/mcp-app.tsx |
Before writing any code, analyze the server's existing tools and determine which ones benefit from UI.
| Tool output type | UI benefit | Example |
|---|---|---|
| Structured data / lists / tables | High — interactive table, search, filtering | List of items, search results |
| Metrics / numbers over time | High — charts, gauges, dashboards | System stats, analytics |
| Media / rich content | High — viewer, player, renderer | Maps, PDFs, images, video |
| Simple text / confirmations | Low — text is fine | "File created", "Setting updated" |
| Data for other tools | Consider app-only | Polling endpoints, chunk loaders |
npm install @modelcontextprotocol/ext-apps
npm install -D vite vite-plugin-singlefile
Plus framework-specific dependencies if needed (e.g., react, react-dom, @vitejs/plugin-react for React).
Use npm install to add dependencies rather than manually writing version numbers. This lets npm resolve the latest compatible versions. Never specify version numbers from memory.
Create vite.config.ts with vite-plugin-singlefile to bundle the UI into a single HTML file:
import { defineConfig } from "vite";
import { viteSingleFile } from "vite-plugin-singlefile";
export default defineConfig({
plugins: [viteSingleFile()],
build: {
outDir: "dist",
rollupOptions: {
input: "mcp-app.html", // one per UI, or one shared entry
},
},
});
Create mcp-app.html (or one per distinct UI if tools need different views):
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>MCP App</title>
</head>
<body>
<div id="root"></div>
<script type="module" src="./src/mcp-app.ts"></script>
</body>
</html>
Add build scripts to package.json. The UI must be built before the server code bundles it:
{
"scripts": {
"build:ui": "vite build",
"build:server": "tsc",
"build": "npm run build:ui && npm run build:server",
"serve": "tsx server.ts"
}
}
Transform plain MCP tools into App tools with UI.
Before (plain MCP tool):
server.tool("my-tool", { param: z.string() }, async (args) => {
const data = await fetchData(args.param);
return { content: [{ type: "text", text: JSON.stringify(data) }] };
});
After (App tool with UI):
import { registerAppTool, registerAppResource, RESOURCE_MIME_TYPE } from "@modelcontextprotocol/ext-apps/server";
const resourceUri = "ui://my-tool/mcp-app.html";
registerAppTool(server, "my-tool", {
description: "Shows data with an interactive UI",
inputSchema: { param: z.string() },
_meta: { ui: { resourceUri } },
}, async (args) => {
const data = await fetchData(args.param);
return {
content: [{ type: "text", text: JSON.stringify(data) }], // text fallback for non-UI hosts
structuredContent: { data }, // structured data for the UI
};
});
Key guidance:
content array with a text fallback for text-only clientsstructuredContent for data the UI needs to render_meta.ui.resourceUriRegister the HTML resource so the host can fetch it:
import fs from "node:fs/promises";
import path from "node:path";
const resourceUri = "ui://my-tool/mcp-app.html";
registerAppResource(server, {
uri: resourceUri,
name: "My Tool UI",
mimeType: RESOURCE_MIME_TYPE,
}, async () => {
const html = await fs.readFile(
Prerequisites
Time Estimate
15-45 minutes depending on use case complexity
Steps
Common Pitfalls
✓ Do
✗ Don't
💡 Pro Tips
✓ Use when
Use when skill capabilities match your task, clear ROI on time saved, and you can validate outputs. Best for repetitive tasks, learning, and quality improvement.
✗ Avoid when
Avoid when task requires deep expertise you can't validate, involves sensitive decisions, or when learning process is more valuable than speed of completion.
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add-app-to-server has been reliable in day-to-day use. Documentation quality is above average for community skills.
Keeps context tight: add-app-to-server is the kind of skill you can hand to a new teammate without a long onboarding doc.
I recommend add-app-to-server for anyone iterating fast on agent tooling; clear intent and a small, reviewable surface area.
Registry listing for add-app-to-server matched our evaluation — installs cleanly and behaves as described in the markdown.
Useful defaults in add-app-to-server — fewer surprises than typical one-off scripts, and it plays nicely with `npx skills` flows.
We added add-app-to-server from the explainx registry; install was straightforward and the SKILL.md answered most questions upfront.
add-app-to-server is among the better-maintained entries we tried; worth keeping pinned for repeat workflows.
Solid pick for teams standardizing on skills: add-app-to-server is focused, and the summary matches what you get after install.
add-app-to-server reduced setup friction for our internal harness; good balance of opinion and flexibility.
add-app-to-server is among the better-maintained entries we tried; worth keeping pinned for repeat workflows.
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