MCP

vercel-labs/mcp

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.

882 tokens

context cost

the whole folder, loaded on every use

files

instructions only

copies elsewhere

how many repositories repackaged it

15821

stars on the repo

on the repository, not the skill itself

Install

one command, takes just this skill from the repository

npx skills add https://github.com/vercel-labs/json-render --skill mcp

The instruction itself

12 sections, as written by the author

@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

createMcpApp() creates an McpServer that registers a render-ui tool and a ui:// HTML resource
The tool description includes the catalog prompt so the LLM knows how to generate valid specs
The HTML resource is a Vite-bundled single-file React app with json-render renderers
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

How to use it

Copy the folder

Take vercel-labs/mcp from the repository into ~/.claude/skills for personal use, or into .claude/skills inside a project.

Check the name does not clash

The agent identifies a skill by the name field in its header. Two skills with the same name cannot sit side by side — one of them will be ignored.

Install what it needs

The instructions reference npm. Without those the skill loads but fails at the first command.

MCP