Show HN: ChatGPT Tamagochi Pet Using Apps SDK (chatagotchi.app)

A developer posted "Chatagotchi," a demo that embeds a Tamagotchi‑style interactive pet inside ChatGPT using the Apps SDK. The pet UI is powered by tools served from an external MCP (Message/Model Connector Provider) server that return structuredContent; ChatGPT’s client-side widgets render that structured content into a rich, interactive experience. To run the demo you need Developer Mode enabled in ChatGPT and a connection to the demo MCP server (URL provided). This is significant because it showcases how the Apps SDK and MCP pattern can move beyond text-only tool calls to deliver stateful, widget-driven interfaces inside chat—think persistent mini‑apps, dashboards, games, or multimodal components that maintain their own UI and state while interacting with a model. For builders and researchers, the key technical takeaway is the structuredContent pipeline: server-side tools produce machine‑readable UI instructions that the ChatGPT client interprets, enabling richer interactions without overloading plain-text prompts. The demo is a proof-of-concept for embedding interactive agents and UIs into chat workflows, illustrating new possibilities for human-AI interfaces, rapid prototyping, and tool-mediated agent behaviors.