MCP Apps: Extending the Frontier — Ido Salomon & Liad Yosef

MCP Apps standardizes the interaction between applications and hosts, extending beyond traditional user-initiated actions. This is achieved through 'view tools,' which allow the host (like a chat interface) to directly interact with an application on behalf of the user – for example, filling out forms automatically. The specification for view tools is currently in development and expected to be released shortly.

MCP apps operate within a spectrum of user interface generation, ranging from predefined UIs (like black box iframes) to declarative UIs (JSON render or A2UI) where the chat builds the UI based on instructions, and finally to fully generative UIs. MCP apps are designed to be agnostic to how the UI is generated, meaning they can support various methods including those used in cloud applications where the host can request a UI generation from the app itself.

The adoption rate of ChatGPT, with its 800 million weekly users (approximately 10% of the global population), demonstrates a significantly accelerated growth compared to the early days of the web. This rapid expansion represents an addressable market roughly 170 times larger than that of the Apple App Store at launch, highlighting the immense potential for MCP apps as a new distribution method.

A key benefit of MCP Apps is their universal compatibility; an application built once can function across various platforms like Libra Chat and ChatGPT. This 'write once, run everywhere' capability simplifies development and distribution, ensuring broad reach and consistent user experience regardless of the underlying platform.

Ido and Adi explain that the reliance on text-based communication within MCP is a significant blocker for companies wanting to build MCP servers. They argue that reducing services to textual databases diminishes brand identity and wastes effort invested in user experience design, as it results in unappealing interfaces. The core issue lies in the inefficiency of conveying information through walls of text.

The speakers propose a solution where applications send their user interfaces directly to chat environments. This allows users to interact with services like Hugging Face within the chat, rather than viewing static textual responses. This approach aims to preserve brand identity and provide a more engaging experience for users by integrating interactive UI chunks into the MCP environment.

Ido introduces MCPUI, described as an open protocol for interactive applications over MCP. It not only defines how UI is transmitted but also establishes a standardized method for that UI and the application to communicate with the host system. This allows for interaction between users and services within the chat environment while maintaining control of the flow by the host.

MCP apps have seen rapid adoption across various platforms, including ChatGPT, VS Code, Shopify, 11 Labs, Postman, Goose (now integrated into Block’s agentic commerce solution), Cursor, and GitHub. This widespread adoption is further fueled by a growing community building plugins, integrations, and educational courses around the MCP apps protocol, demonstrating its increasing importance in the ecosystem.