Internet-Drafts

The specification is the authortative document on JSON Schema, targeted at authors of validators. The latest draft is v4. The specification is split into three parts:

JSON Schema Core defines the basic foundation of JSON Schema
JSON Schema Validation defines the validation keywords of JSON Schema
JSON Hyper-Schema defines the hyper-media keywords of JSON Schema

They are also available as Internet Drafts on the IETF site: core, validation and hyper-schema.

Meta-schemas

The meta-schemas are the schemas which define the JSON Schema and Hyper-Schema formats.

Core/Validation Meta-Schema Used for schemas written for pure validation.
Hyper Meta-Schema Used for schemas written for validation and hyper-linking.