TOON (Token‑Oriented Object Notation) is a compact, LLM‑friendly format that typically reduces token count by 30–60% vs JSON. Fewer tokens = lower costs and more room in the context window.

• Fewer tokens → lower cost: Keys aren’t repeated for every row.
• More context per request: Save tokens for what matters (instructions + data).
• LLM‑friendly structure: Simple, row‑oriented text with predictable patterns.

1. Declare keys once per uniform array: {id,name,role} instead of repeating keys.
2. State length upfront: [3] clearly signals row count.
3. Minimal syntax: Avoids braces/quotes unless needed (quotes only when required).
4. Delimited rows: Values appear in a fixed key order (CSV/TSV‑like), which tokenizes well.

Example

// JSON
{
  "users": [
    { "id": 1, "name": "Alice", "role": "admin" },
    { "id": 2, "name": "Bob", "role": "user" }
  ]
}

// TOON
users[2]{id,name,role}:
  1,Alice,admin
  2,Bob,user

Use TOON when your data is:

• Uniform arrays of objects (same keys per row)
• Flat or shallow (1–2 nesting levels)
• Large and sent directly to an LLM

• Non‑uniform arrays (varying keys across rows)
• Deeply nested objects (>3 levels) where readability drops
• General storage/transport for arbitrary data (JSON/MsgPack are better)
• Schemas with many optional fields (header becomes sparse/misleading)

Prereqs: Node.js 18+. Ollama optional for local model tests.

Install

npm install

Run

npm start          # Quick comparison (JSON vs TOON)
npm run compare    # Detailed metrics (bytes, lines, tokens)
npm run test       # Test with an Ollama model (if installed)

Example Results:

• Detailed Comparison Results - Token counts, byte sizes, and format comparisons across multiple datasets
• LLM Test Results - Real-world testing with Ollama (llama3.1:8b) showing response times and token usage

Use in Code

import { encode } from './src/toon.js';

const data = { users: [
  { id: 1, name: 'Alice', role: 'admin' },
  { id: 2, name: 'Bob', role: 'user' }
]};

console.log(encode(data));                 // default comma delimiter
console.log(encode(data, { delimiter: '\t' })); // often tokenizes better

Notes

• Token counting uses tiktoken. Actual savings depend on model/tokenizer.
• Delimiters supported: comma, tab, pipe. Tab often yields best tokenization.
• TOON is designed for LLM prompts, not as a general‑purpose data store.

Apache License 2.0