Kwalify

Kwalify is an open-source data validation tool and schema language for YAML and JSON. It provides a way to express the expected structure and constraints of data in a YAML-based schema and then validate data files against that schema. It is commonly used to verify configuration files and data payloads in software projects to catch formatting and type errors early.

The Kwalify schema is written in YAML and describes the types, required fields, allowed values, and constraints for maps, sequences, and scalars, including nested structures. The validator reports errors with location information to help pinpoint how data fails to conform to the schema. It supports enforcing primitive types (string, number, boolean) as well as complex structures, optional fields, default values, and value constraints such as patterns and enumerations. The tool can validate both YAML and JSON input against the same schema.

Kwalify originated as an open-source project with a reference implementation in Ruby; over time, ports and bindings have appeared for other languages in the ecosystem. It is typically used as a command-line utility or as a library integrated into applications that require strict configuration validation or data integrity checks.

See also:

- JSON Schema

- YAML

- Data validation libraries