MCP Apps vs. OpenAI Apps SDK

For the past year, the AI industry has faced a “connectivity crisis.” Developers were forced to build custom, proprietary connectors for every different AI model and tool, a mess known as the “N×M” integration problem.

The Model Context Protocol (MCP) changed that by acting as the “USB-C port for AI,” providing a universal way to connect models to data. But the newest evolution, MCP Apps, takes this a step further by adding a visual, interactive layer to these connections.

What exactly are MCP Apps?

MCP Apps are an official extension to the Model Context Protocol that enables AI servers to deliver rich, interactive user interfaces directly inside AI chat windows.

Instead of an assistant just giving you a “wall of text,” an MCP App allows the tool to render a functional widget: like a live sales dashboard, a draggable project timeline, or a data visualization, inside a sandboxed environment within your conversation.

How MCP Apps Work: The Technical Engine

The architecture relies on a Client-Host-Server model designed for both flexibility and security:

• The Host: The primary application the user interacts with (e.g., ChatGPT, Claude Desktop, or VS Code).
• The Server: A program that hosts the data and the UI templates. It uses a specific URI scheme, ui://, to tell the host where to find the interactive interface.
• The Communication: Unlike older proprietary systems, MCP Apps use a standardized JSON-RPC protocol over postMessage to let the UI talk to the AI model in real-time.
• The Sandbox: For security, these apps run in “double iframes.” This ensures that a third-party app cannot “hack” the host application or access your private browser data.

Comparison: MCP Apps vs. OpenAI Apps SDK (GPT Apps)

Before the industry converged on a single standard, OpenAI led with its proprietary Apps SDK. While the user experience is similar, the underlying philosophy and portability are vastly different.

Feature	OpenAI Apps SDK (GPT Apps)	MCP Apps (Open Standard)
Portability	Limited primarily to the ChatGPT ecosystem.	Multi-platform: Works in Claude, ChatGPT, Cursor, and VS Code.
UI Metadata	Uses _meta.openai/outputTemplate.	Uses the standard _meta.ui.resourceUri.
Governance	Proprietary to OpenAI.	Managed by the Linux Foundation’s Agentic AI Foundation (AAIF).
Development	Requires OpenAI-specific widget runtimes.	Uses pure MCP with a standardized UI extension.

Why the Industry is Shifting to MCP

The convergence has happened remarkably fast. In March 2025, OpenAI officially adopted the Model Context Protocol for ChatGPT, signaling a shift away from proprietary “walled gardens” toward an open ecosystem.

For developers, the win is “Build Once, Deploy Anywhere.” An MCP App built today doesn’t just work in a single chat window; it is designed to render in any environment, whether that’s a mobile app, a desktop terminal, or a coding IDE.

The Road Ahead: Agentic Commerce

Looking toward 2026, the synergy between MCP and other protocols like the Universal Commerce Protocol (UCP) is creating a new era of “Agentic Commerce”. In this future, your AI agent won’t just find a product for you, it will use an MCP App to show you a technical comparison, verify specifications via an interactive widget, and execute the purchase autonomously.

Key Takeaway for Developers

If you are building interactive AI experiences today, MCP Apps provide the most future-proof path. By following the official open standard, you ensure your tools remain compatible with the rapidly growing directory of thousands of MCP-enabled hosts and servers.