If you've ever tried to do serious code generation from JSON Schema — or used OpenAPI tooling on a complex schema and watched it give up mid-object — you've felt the same frustration that drove Clemens Vasters to build something new. Clemens is a principal architect at Microsoft working on Fabric, the messaging and real-time intelligence platform. He needs schemas that work as data definition languages: things you can generate code from, land in database columns, feed to LLMs with enough fidelity that the LLM can reason about the data correctly. JSON Schema is designed to validate documents. Those are not the same job. I talked with him twice — in February and again this week — and came away with a clear picture of what JSON Structure is and why it matters. Here's the short version. What's wrong with JSON Schema JSON Schema's compositional constructs ( anyOf , allOf , oneOf ) are expressive but carry no semantic guarantees.…