Schema

• REST API uses JSON Schema (draft 4 subset) for resource and argument definitions.
• Provide schema via get_item_schema() on controllers or schema callbacks on routes.
• Schema enables discovery (OPTIONS) and validation.

Validation + sanitization

• Use rest_validate_value_from_schema( $value, $schema ) then rest_sanitize_value_from_schema( $value, $schema ).
• If you override sanitize_callback, built-in schema validation will not run; use rest_validate_request_arg to keep it.
• WP_REST_Controller::get_endpoint_args_for_item_schema() wires validation automatically.

Schema caching

• Cache the generated schema on the controller instance ($this->schema) to avoid recomputation.

Formats and types

• Common formats: date-time, uri, email, ip, uuid, hex-color.
• For array and object types, you must define items or properties schemas.