# TOON

> TOON (Token-Oriented Object Notation) is a compact, human-readable encoding of the JSON data model for LLM prompts, with a TypeScript SDK and CLI.

TOON (Token-Oriented Object Notation) is an open-source, MIT-licensed format for passing structured data to large language models in fewer tokens. The project provides a TypeScript SDK, a CLI, a playground and benchmarks, and the current release is v4.4.0.

## What It Is

TOON is a serialization format that encodes the same objects, arrays and primitives as JSON, with deterministic, lossless round-trips. It uses indentation instead of braces and minimizes quoting, which the site describes as YAML-like readability with CSV-style compactness. It is meant for LLM prompts and outputs rather than as a general replacement for JSON in every context.

## How the Format Works

Uniform objects, whether in an array or under keys, use a tabular form: the field list is declared once and each object follows as a single row. Array headers declare the row count with [N] and the field names with {fields}, so the site says truncated or malformed output cannot slip through unnoticed. The documentation describes four forms of the format, along with quoting and type rules.

## Efficiency Claims

The project's benchmarks page states that TOON matches JSON's retrieval accuracy (72.2% vs 71.4%) while using 42.6% fewer tokens. These are figures published by the project itself.

## Tooling and Ecosystem

The documentation covers a getting-started guide, guidance on using TOON with LLMs, a CLI, an API reference, a syntax cheatsheet, a specification and an efficiency formalization. The site says there are official implementations plus dozens of community ports, all targeting one spec with a shared conformance test suite.

## Features
- Compact, human-readable encoding of the JSON data model
- Deterministic, lossless JSON round-trips
- Tabular form for uniform object arrays
- Array headers declaring row count [N] and fields {fields}
- Indentation-based minimal syntax
- TypeScript SDK
- CLI
- Online playground
- Benchmarks
- Shared conformance test suite across implementations

## Platforms
WEB, API, DEVELOPER_SDK, CLI

## Pricing
Open Source

## Version
v4.4.0

## Links
- Website: https://toonformat.dev
- Documentation: https://toonformat.dev/guide/getting-started.html
- Repository: https://github.com/toon-format/toon
- EveryDev.ai: https://www.everydev.ai/tools/toon