Specification

The latest IETF published draft is v3. However, a newer version of the specification is being prepared for submission in early 2013.

The latest specifications are available here:

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

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.

Standard schemas

These sample schemas describe simple data structures which can be expressed as JSON:

Geographic Coordinate a location as longitude and latitude
Card a microformat-style representation of a person, company, organization, or place
Calendar a microformat-style representation of an event
Address a microformat-style representation of a street address