TOONToken-Oriented Object Notation

A compact, human-readable encoding of the JSON data model for LLM prompts.

What is TOON?

Benchmarks

Playground

CLI

📊

Token-Efficient & Accurate

TOON reaches 72.2% accuracy (vs JSON's 71.4%) while using 42.6% fewer tokens across 244 retrieval questions on 4 models.

🔁

JSON Data Model

Encodes the same objects, arrays, and primitives as JSON with deterministic, lossless round-trips.

🛤️

LLM-Friendly Guardrails

Explicit [N] lengths and {fields} field lists in every header give models a clear schema to follow, improving parsing reliability.

📐

Minimal Syntax

Uses indentation instead of braces and minimizes quoting, giving YAML-like readability with CSV-style compactness.

🧺

Tabular Forms

Uniform arrays of objects – and objects of uniform objects – collapse into tables that declare the field list once and stream row values line by line.

🌐

Multi-Language Ecosystem

Spec-driven implementations in many languages.