TOON

TOON (Token-Oriented Object Notation): The compact, human-readable data serialization format engineered to reduce Large Language Model (LLM) token costs by 30-60% versus verbose JSON.

TOON is a lossless, token-efficient data serialization format, purpose-built for optimizing LLM context windows. It functions as a drop-in representation of the JSON data model, utilizing a hybrid structure: YAML-like indentation for nested objects and a CSV-style tabular layout for uniform arrays (e.g., lists of 100 customer records). This design eliminates repetitive syntax like braces and quotes, yielding a measured 30-60% reduction in tokens for LLM input. The format is designed for reliable parsing and validation by models like GPT-4, with a reference implementation available in TypeScript/JavaScript.

https://toon-format.vercel.app/