StemJSON is a new declarative language based on JSON designed to simplify the development and delivery of native mobile applications. The language is optimized for use by AI to generate comprehensive UI and logic, allowing for the creation of new apps or the extension of existing ones.

The language works by turning descriptions into native components, which can be rendered on-device via iOS and Android runtimes. One primary use case is a "Stem AI Area," where an LLM processes a user's prompt to emit StemJSON, which the runtime then validates and renders as a native module within a defined sandbox. This process avoids the need for new binaries or backend round-trips for UI updates.

Developers can also push complete functional modules—including state, actions, expressions, and navigation—directly from a backend to a device. Additionally, StemJSON supports a workflow where tools such as Figma or AI assistants emit StemJSON to create runnable native prototypes. The language is designed to be integrated into existing native codebases through Swift or Kotlin SDKs, enabling the addition of new screens without requiring app updates.

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