/mcp

name: mcp
description: MCP Apps integration for json-render. Use when building MCP servers that render interactive UIs in Claude, ChatGPT, Cursor, or VS Code, or when integrating json-render with the Model Context Protocol.

@json-render/mcp

MCP Apps integration that serves json-render UIs as interactive MCP Apps inside Claude, ChatGPT, Cursor, VS Code, and other MCP-capable clients.

Quick Start

Server (Node.js)

import { createMcpApp } from "@json-render/mcp";
import { defineCatalog } from "@json-render/core";
import { schema } from "@json-render/react/schema";
import { shadcnComponentDefinitions } from "@json-render/shadcn/catalog";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import fs from "node:fs";

const catalog = defineCatalog(schema, {
  components: { ...shadcnComponentDefinitions },
  actions: {},
});

const server = createMcpApp({
  name: "My App",
  version: "1.0.0",
  catalog,
  html: fs.readFileSync("dist/index.html", "utf-8"),
});

await server.connect(new StdioServerTransport());

Client (React, inside iframe)

import { useJsonRenderApp } from "@json-render/mcp/app";
import { JSONUIProvider, Renderer } from "@json-render/react";

function McpAppView({ registry }) {
  const { spec, loading, error } = useJsonRenderApp();
  if (error) return <div>Error: {error.message}</div>;
  if (!spec) return <div>Waiting...</div>;
  return (
    <JSONUIProvider registry={registry} initialState={spec.state ?? {}}>
      <Renderer spec={spec} registry={registry} loading={loading} />
    </JSONUIProvider>
  );
}

Architecture

1. `createMcpApp()` creates an `McpServer` that registers a `render-ui` tool and a `ui://` HTML resource 2. The tool description includes the catalog prompt so the LLM knows how to generate valid specs 3. The HTML resource is a Vite-bundled single-file React app with json-render renderers 4. Inside the iframe, `useJsonRenderApp()` connects to the host via `postMessage` and renders specs

Server API

• `createMcpApp(options)` - main entry, creates a full MCP server
• `registerJsonRenderTool(server, options)` - register a json-render tool on an existing server
• `registerJsonRenderResource(server, options)` - register the UI resource

Client API (`@json-render/mcp/app`)

• `useJsonRenderApp(options?)` - React hook, returns `{ spec, loading, connected, error, callServerTool }`
• `buildAppHtml(options)` - generate HTML from bundled JS/CSS

Building the iframe HTML

Bundle the React app into a single self-contained HTML file using Vite + `vite-plugin-singlefile`:

// vite.config.ts
import { defineConfig } from "vite";
import react from "@vitejs/plugin-react";
import { viteSingleFile } from "vite-plugin-singlefile";

export default defineConfig({
  plugins: [react(), viteSingleFile()],
  build: { outDir: "dist" },
});

Client Configuration

Cursor (`.cursor/mcp.json`)

{
  "mcpServers": {
    "my-app": {
      "command": "npx",
      "args": ["tsx", "server.ts", "--stdio"]
    }
  }
}

Claude Desktop

{
  "mcpServers": {
    "my-app": {
      "command": "npx",
      "args": ["tsx", "/path/to/server.ts", "--stdio"]
    }
  }
}

Dependencies

# Server
npm install @json-render/mcp @json-render/core @modelcontextprotocol/sdk

# Client (iframe)
npm install @json-render/react @json-render/shadcn react react-dom

# Build tools
npm install -D vite @vitejs/plugin-react vite-plugin-singlefile