mCP Apps are a standard for delivering interactive HTML interfaces directly from an mCP server into a chat conversation to enhance user exploration.
An Express server is configured with an mCP endpoint to register a primary app resource that serves the HTML for the to-do list UI.
Three distinct tools are registered on the server to handle listing all to-dos, creating a new item with Zod schema validation, and toggling an item's completion status.
The React component uses `window.parent.postMessage` to send tool call requests from the rendered UI back to the LLM client.
The local server is exposed via a proxy tunnel and added as a connector in Claude AI, revealing a UI refresh issue during the initial test.
A `message` event listener is added to the React component to receive tool output from the LLM, enabling the UI to update its state and re-render with the latest data.
Jobs that call for the skills explored in this talk.