TOON format spec and syntax

TOON expresses any JSON value using indentation instead of brackets. This reference covers each rule with a short example. Conversion is lossless in both directions — valid JSON maps to TOON and back without changing a single value.

Objects

Keys are written one per line as key: value. Keys are unquoted when they are simple identifiers (letters, digits, underscores, hyphens) and quoted otherwise.

name: Ada
role: engineer
"display name": Ada Lovelace

Nesting

A nested object goes on the following lines, indented by two spaces:

user:
  id: 1
  address:
    city: London
    zip: EC1A

Arrays of objects

Each element starts with a dash. Fields of the same object align under it. This is where TOON saves the most versus JSON, because the field names are not repeated as punctuation.

items:
  - id: 1
    name: Pen
  - id: 2
    name: Pencil

Simple (scalar) arrays

Short arrays of primitives are written inline in square brackets, space-separated. Longer ones break onto dashed lines.

tags: [red green blue]

Strings

A string is left unquoted when it is a simple token. Strings containing spaces or special characters are wrapped in double quotes, and inner quotes are escaped with a backslash.

title: Hello
note: "needs a comma, so it is quoted"

Numbers, booleans, and null

These are written bare, exactly as in JSON:

count: 42
ratio: 3.14
active: true
deleted: null

Empty values

An empty object is {} and an empty array is [].

Convert without reading the spec

You rarely need to write TOON by hand. Paste JSON into the converter and it produces valid TOON for you instantly, in your browser.