toon

toon-format/toon is an open-source project by toon-format: 🎒 Token-Oriented Object Notation (TOON) – compact, human-readable serialization of JSON data for LLM prompts. TypeScript SDK, CLI, benchmarks.. Indexed here so it can be found — not resold.

It is free. Get it from the upstream repository: https://github.com/toon-format/toon

From the project's own README (excerpt, reproduced for discovery under its MIT license):

Token-Oriented Object Notation (TOON)

Token-Oriented Object Notation is a compact, human-readable encoding of the JSON data model that minimizes tokens and makes structure easy for models to follow.

TOON combines YAML's indentation-based structure for nested objects with CSV-style tabular forms for uniform data. Its sweet spot is uniform objects – same fields across items, whether in an array or keyed by ID – reaching CSV-like compactness while adding explicit structure that helps LLMs parse and validate data reliably. For deeply nested or non-uniform data, JSON may be more efficient.

Think of it as a translation layer: use JSON programmatically, and encode it as TOON for LLM input – a drop-in, lossless representation of the JSON you already have.

> The TOON format is stable, but also an idea in progress. Nothing's set in stone – help shape where it goes by contributing to the spec or sharing feedback.

Table of Contents • Why TOON? • Key Features • When Not to Use TOON • Benchmarks • Installation & Quick Start • CLI • Using TOON with LLMs • Ecosystem • Documentation • Media Type & File Extension • 📋 Full Specification

Why TOON?

LLM tokens cost money – and JSON spends a lot of them on structure. A weather forecast in TOON:

The same data as JSON – ~117 tokens against TOON's ~66:

Three things are happening at once in the TOON above. Two are forms – one rendering of a value, picked automatically from the data's shape – and the third is a header feature: • alerts[2]: frost,wind is inline form: a primitive array on its header line. • forecast[3]{day,…}: is tabular form: the field list is declared once in the header, then one row per element. • temp{min,max} inside that header is a nested field group: the uniform nested temp objects fold into the…