toon

Encode-only Go implementation of TOON (Token-Oriented Object Notation), spec v3.3.

TOON is a line-oriented, indentation-based text format for the JSON data model. Compared with JSON it drops most punctuation, and arrays of uniform objects collapse to a single field header plus one delimited row per element — typically ~40% fewer LLM tokens than JSON for list-shaped data.

Install

go get github.com/moonrhythm/toon

Usage

b, err := toon.Marshal(v)

Marshal interprets v using encoding/json semantics — json struct tags (omitempty, -, renames) and custom MarshalJSON implementations are honored — then renders TOON. Anything that marshals correctly to JSON marshals correctly to TOON, with object key order and full number precision preserved.

type User struct {
	ID    int    `json:"id"`
	Name  string `json:"name"`
	Email string `json:"email"`
}

b, _ := toon.Marshal(map[string]any{
	"users": []User{
		{1, "Alice", "alice@example.com"},
		{2, "Bob", "bob@example.com"},
	},
})

users[2]{id,name,email}:
  1,Alice,alice@example.com
  2,Bob,bob@example.com

toon.MediaType (text/toon) is the format's provisional media type, for HTTP content negotiation.

Empty fields are omitted by default

Empty object fields — null, "", {}, [] (after their own contents are pruned) — are omitted from the output: absent and empty carry the same information for an LLM reader, and empty fields are pure token cost. false and 0 are meaningful values and are always kept, and array elements are never removed.

In an array of objects, a field is omitted only when it is empty in every element — per-element omission would break the key-set uniformity that enables the tabular layout (and cost more tokens than it saves).

Pass toon.IncludeEmpty() to encode the full data model verbatim:

b, err := toon.Marshal(v, toon.IncludeEmpty())

Format choices

Output is deterministic with fixed spec-default options: 2-space indent, comma delimiter, length markers on, no key folding. There is no decoder — the format targets LLM consumers, which read it natively.

Conformance

The test suite includes the official encoder fixtures from the spec repository, and the encoder's output for every fixture plus an adversarial corpus round-trips cleanly through the reference TypeScript implementation's strict decoder.

License

MIT