toon/docs/reference/syntax-cheatsheet.md

Syntax Cheatsheet

Quick reference for mapping JSON to TOON format. For rigorous, normative syntax rules and edge cases, see the Specification.

Objects

::: code-group

{
  "id": 1,
  "name": "Ada"
}

id: 1
name: Ada

:::

Nested Objects

::: code-group

{
  "user": {
    "id": 1,
    "name": "Ada"
  }
}

user:
  id: 1
  name: Ada

:::

Primitive Arrays

::: code-group

{
  "tags": ["foo", "bar", "baz"]
}

tags[3]: foo,bar,baz

:::

Tabular Arrays

::: code-group

{
  "items": [
    { "id": 1, "qty": 5 },
    { "id": 2, "qty": 3 }
  ]
}

items[2]{id,qty}:
  1,5
  2,3

:::

Mixed / Non-Uniform Arrays

::: code-group

{
  "items": [1, { "a": 1 }, "x"]
}

items[3]:
  - 1
  - a: 1
  - x

:::

Note

When a list-item object has a tabular array as its first field, the tabular header appears on the hyphen line. Rows are indented two levels deeper than the hyphen, and other fields are indented one level deeper. This is the canonical encoding for this pattern.

::: code-group

items[1]:
  - users[2]{id,name}:
      1,Ada
      2,Bob
    status: active

items[1]:
  - users[2]{id,name}:
      1,Ada
      2,Bob

:::

Arrays of Arrays

::: code-group

{
  "pairs": [[1, 2], [3, 4]]
}

pairs[2]:
  - [2]: 1,2
  - [2]: 3,4

:::

Root Arrays

::: code-group

["x", "y", "z"]

[3]: x,y,z

:::

Empty Containers

::: code-group

{}

(empty output)

:::

::: code-group

{
  "items": []
}

items[0]:

:::

Quoting Special Cases

Strings That Look Like Literals

::: code-group

{
  "version": "123",
  "enabled": "true"
}

version: "123"
enabled: "true"

:::

These strings must be quoted because they look like numbers/booleans.

Strings with Active Delimiter

::: code-group

{
  "note": "hello, world"
}

note: "hello, world"

:::

Strings containing the active delimiter (comma by default) must be quoted.

Strings with Leading/Trailing Spaces

::: code-group

{
  "message": " padded "
}

message: " padded "

:::

Empty String

::: code-group

{
  "name": ""
}

name: ""

:::

Quoting Rules Summary

Strings must be quoted if they:

• Are empty ("")
• Have leading or trailing whitespace
• Equal true, false, or null (case-sensitive)
• Look like numbers (e.g., "42", "-3.14", "1e-6", "05")
• Contain special characters: :, ", \, [, ], {, }, newline, tab, carriage return
• Contain the active delimiter (comma by default, or tab/pipe if declared in header)
• Equal "-" or start with "-" followed by any character

Otherwise, strings can be unquoted. Unicode and emoji are safe:

message: Hello 世界 👋
note: This has inner spaces

Escape Sequences

Only five escape sequences are valid in quoted strings:

Character	Escape
Backslash (\)	\\
Double quote (")	\"
Newline	\n
Carriage return	\r
Tab	\t

All other escapes (e.g., \x, \u) are invalid.

Array Headers

Basic Header

key[N]:

• N = array length
• Default delimiter: comma

Tabular Header

key[N]{field1,field2,field3}:

• N = array length
• {fields} = column names
• Default delimiter: comma

Alternative Delimiters

::: code-group

items[2	]{id	name}:
  1	Alice
  2	Bob

items[2|]{id|name}:
  1|Alice
  2|Bob

:::

The delimiter symbol appears inside the brackets and braces.

Key Folding (Optional)

Standard nesting:

data:
  metadata:
    items[2]: a,b

With key folding (keyFolding: 'safe'):

data.metadata.items[2]: a,b

See Format Overview – Key Folding for details.

Type Conversions

Input	Output
Finite number	Canonical decimal (no exponent, no trailing zeros)
NaN, Infinity, -Infinity	null
BigInt (safe range)	Number
BigInt (out of range)	Quoted decimal string
Date	ISO string (quoted)
undefined, function, symbol	null