What is TOON?

Token-Oriented Object Notation (TOON) is a compact, human-readable, schema-aware JSON format designed for LLM prompts. It's more token-efficient than JSON while maintaining readability.

Official Specification

Overview

Understanding the Toon format

Toon format is specifically designed for LLM (Large Language Model) prompts where token efficiency and human readability matter. It provides a compact representation of JSON data that's easier for both humans and AI models to parse.

Unlike raw JSON, Toon uses schema-aware encoding with explicit array lengths, field headers, and tabular formatting for uniform data structures. This makes it particularly efficient for representing arrays of objects with identical keys.

Key Features

Token-efficient: More compact than JSON for LLM prompts
Schema-aware: Explicit array lengths and field headers
Human-readable: Clean, indented structure
Tabular format: Optimized for uniform arrays of objects
Self-descriptive: Array headers show structure clearly

Examples

See how JSON converts to Toon format

Example 1: Simple Object

Input (JSON):

{
  "id": 1,
  "name": "Alice",
  "role": "admin"
}

Output (Toon):

id: 1
name: Alice
role: admin

Example 2: Tabular Array (Uniform Objects)

Input (JSON):

{
  "items": [
    { "sku": "A1", "qty": 2, "price": 9.99 },
    { "sku": "B2", "qty": 1, "price": 14.5 }
  ]
}

Output (Toon):

items[2]{sku,qty,price}:
  A1,2,9.99
  B2,1,14.5

Notice the array header items[2]{sku,qty,price}:shows the length (2) and field names, making it self-descriptive.

Example 3: Nested Structure

Input (JSON):

{
  "name": "Toonade",
  "version": "1.0.0",
  "config": {
    "theme": "auto",
    "language": "en"
  }
}

Output (Toon):

name: Toonade
version: 1.0.0
config:
  theme: auto
  language: en

Usage

Step 1: Paste JSON

Copy and paste your JSON data into the input field on the homepage.

Step 2: Convert

Click the "Convert to Toon" button to transform your JSON into Toon format using the official @toon-format/toon SDK.

Step 3: Copy

Use the copy button to quickly copy the converted Toon output to your clipboard. Perfect for use in LLM prompts!

Best Use Cases

LLM Prompts: More token-efficient than JSON for AI model inputs
Uniform Arrays: Especially efficient for arrays of objects with identical keys
Data Visualization: Clean, readable format for documentation
Schema-Aware Data: When you need explicit structure information

Tips

Make sure your JSON is valid before converting
Toon format excels with uniform arrays of objects (same fields)
For non-uniform data, Toon may use list format which is still readable
The format uses 2-space indentation by default
Check out the official specification for advanced features like custom delimiters