JSON Schema
JSON Schema is a declarative language for annotating and validating JSON documents. It is the foundational schema language for most modern API specifications (OpenAPI 3.1, AsyncAPI 3, and others embed it directly). The current stable dialect is Draft 2020-12. Governance is moving toward a chartered standards body (JSON Schema Foundation), with the IETF as the historical sponsor; reference implementations and tooling are MIT and BSD-licensed.