JSON-io – Java library for JSON, JSON5, and TOON (40% fewer LLM tokens)

I built TOON support into json-io, a Java serialization library. TOON is an indentation-based format designed for LLM applications where every token costs money and eats context window.

Same data as JSON, ~40-50% fewer tokens. No braces, brackets, commas, or unnecessary quoting. Arrays of uniform objects become CSV-like tables automatically.

JSON: {"team":"Rockets","players":[{"name":"John","age":30},{"name":"Sue","age":27}]}

TOON: team: Rockets players: name, age John, 30 Sue, 27

json-io reads/writes JSON, JSON5, and TOON with 60+ built-in Java types, cycle support, and zero config. There's also a Spring Boot starter and Spring AI module.

GitHub: https://github.com/jdereg/json-io TOON spec: https://toonformat.dev Baeldung article: https://www.baeldung.com/java-json-toon-format-libraries