Okyline Data Design Hub

Okyline is a JSON-based schema language for validating JSON documents by example. You write real example data, then declare constraints directly in field names.

Okyline was designed to express structural validation, conditional rules, and business invariants in a single, readable schema — without splitting logic between schemas, code, and documentation.

All resources available on this hub — including Okyline Free Studio and the Java validation library — can be used free of charge to validate API and microservice payloads, in your business applications, including in production.

The same Okyline language is also used by Okyline Enterprise to validate, analyze, and certify data quality at scale across JSON, JSON Lines, CSV, fixed-width formats, and XML, processing millions of records with full traceability. Enterprise ↗

User Guides

Getting Started

Practical introduction to Okyline: first steps, key concepts, and examples.

Quick Reference

Core Language Quick Reference

Compact reference guide: syntax, types, operators, and common examples.

Specification

Core Language Specification

Complete specification of the Okyline language: syntax, types, constraints, and semantics.

Annex C - Expression Language

Deterministic language for expressing computed validations, business invariants such as cross-field calculations and conditional logic based on field values

Annex D - Internal References

Internal reference mechanism for composing and reusing schema fragments within a single document.

Annex E - External Imports

Cross-schema reference mechanism with identifiers and version management for composing and reusing schema fragments in multiple schemas.

Annex F - Virtual Fields

Allows scenarios in which conditional rules depend on derived values that are not present in the validated data, such as calculated levels, classifications, or indicators.

Resources & Tools

Okyline Web Site↗

Official Okyline website.

Okyline Free Studio↗

Online editor with live validation, JSON Schema generation and documentation preview.

Java library on Maven Central↗

Lightweight and simple Java library (no dependencies) to validate your APIs or microservice payloads with Okyline.

Claude Code Skill↓

Expert assistant for the Okyline data validation language. Use it to create, modify, and convert schemas (from JSON Schema, Avro, etc.) or learn Okyline.