MCP App Builder

Build new MCP Apps (MCP servers with React UI output) using @modelcontextprotocol/ext-apps and the M

Codex

What to use it for

Build new MCP Apps (MCP servers with React UI output) using @modelcontextprotocol/ext-apps and the MCP SDK. Use when asked to scaffold or implement MCP App servers, add UI-rendering tools/resources, or migrate a standard MCP server to an MCP App with Vite single-file UI bundles.

MCP App Builder

How to install & use

Download

Grab the skill package ZIP file using the button above.

Add to Agent

Extract and move the folder into your AI agent's skills directory.

Start Prompting

Your agent now knows the skill. Just ask it to perform the task!

Developer & Source DetailsView raw SKILL.md definition and repository files for advanced usage

Skill Definition (SKILL.md)

This is the raw instruction document consumed by your AI agent.

MCP App Builder

Overview

Create MCP Apps that expose tools with visual React UIs for ChatGPT or Claude. Follow the exact dependency versions and server/UI patterns in references/mcp-app-spec.md.

Workflow

Clarify requirements: what data to visualize, UI pattern (card, table, chart, dashboard, form), data source, and how many tools (start with 1-2).
Design tools and UI mapping: define tool names, zod input schemas, output shape, and UI resource URIs (ui://.../app.html). Map each tool to one React entrypoint and one HTML file.
Scaffold the project: start from assets/mcp-app-template/ when possible, then customize tool names, schemas, and UI. Ensure package.json uses the exact versions, plus tsconfig.json, vite.config.ts, Tailwind + PostCSS, and per-tool build scripts.
Implement the server: use registerAppTool/registerAppResource, zod schemas directly, createServer() factory per request, and createMcpExpressApp with app.all("/mcp", ...).
Implement the UI: use useApp + useHostStyles, parse tool results, handle loading/error/empty states, and apply safe-area insets.
Build and test: run npm run build, then npm run serve, then verify via a tunnel if needed.

Hard Requirements

Use the exact dependency versions listed in references/mcp-app-spec.md.
Use registerAppTool/registerAppResource and zod schemas directly (not JSON Schema objects).
Create a new McpServer instance per request via createServer().
Use createMcpExpressApp and app.all("/mcp", ...).
Bundle UI into single-file HTML via vite-plugin-singlefile.
Use host CSS variables for theme compatibility.

References

references/mcp-app-spec.md (authoritative spec, patterns, code templates, gotchas)

Assets

assets/mcp-app-template/ (ready-to-copy MCP App skeleton with one tool + UI)

Repository Files

Browse additional components, config blocks, and reference sheets included in the ZIP.

skills/mcp-app-builder/agents/openai.yaml

interface:
  display_name: "MCP App Builder"
  short_description: "Create MCP apps with React UIs and tools"
  default_prompt: "Use $mcp-app-builder to scaffold a new MCP App with UI tools."