GoTOON is a Go implementation of TOON (Token-Oriented Object Notation), a compact, human-readable format designed for passing structured data to Large Language Models with significantly reduced token usage.

TOON excels at uniform complex objects – multiple fields per row, same structure across items. It achieves 30-60% token reduction compared to JSON while maintaining high LLM comprehension accuracy.

LLM tokens cost money, and standard JSON is verbose and token-expensive:

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

TOON conveys the same information with fewer tokens:

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

• 💸 Token-efficient: typically 30–60% fewer tokens than JSON
• 🤿 LLM-friendly guardrails: explicit lengths and field lists help models validate output
• 🍱 Minimal syntax: removes redundant punctuation (braces, brackets, most quotes)
• 📐 Indentation-based structure: replaces braces with whitespace for better readability
• 🧺 Tabular arrays: declare keys once, then stream rows without repetition
• 🛠️ Go-idiomatic API: clean, simple interface with functional options

go get github.com/alpkeskin/gotoon

package main

import (
    "fmt"
    "log"

    "github.com/alpkeskin/gotoon"
)

func main() {
    data := map[string]interface{}{
        "users": []map[string]interface{}{
            {"id": 1, "name": "Alice", "role": "admin"},
            {"id": 2, "name": "Bob", "role": "user"},
        },
    }

    encoded, err := gotoon.Encode(data)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(encoded)
}

Output:

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

Converts any Go value to TOON format string.

Input normalization:

• Primitives (bool, int, float, string) are encoded as-is
• Structs are converted to maps using exported fields (respects json tags)
• Slices and arrays remain as arrays
• Maps with string keys remain as objects
• time.Time is converted to RFC3339Nano format
• NaN and Infinity become null
• nil, functions become null

Example:

type User struct {
    ID   int    `json:"id"`
    Name string `json:"name"`
    Role string `json:"role"`
}

users := []User{
    {ID: 1, Name: "Alice", Role: "admin"},
    {ID: 2, Name: "Bob", Role: "user"},
}

encoded, _ := gotoon.Encode(map[string]interface{}{"users": users})
// Output:
// users[2]{id,name,role}:
//   1,Alice,admin
//   2,Bob,user

GoTOON supports functional options for customization:

Sets the number of spaces per indentation level (default: 2).

gotoon.Encode(data, gotoon.WithIndent(4))

Sets the delimiter for array values and tabular rows. Valid values: "," (comma, default), "\t" (tab), "|" (pipe).

// Using tab delimiter
gotoon.Encode(data, gotoon.WithDelimiter("\t"))
// Output:
// users[2	]{id	name	role}:
//   1	Alice	admin
//   2	Bob	user

Adds # prefix to array lengths for clarity (e.g., [#3] instead of [3]).

gotoon.Encode(data, gotoon.WithLengthMarker())
// Output:
// users[#2]{id,name,role}:
//   1,Alice,admin
//   2,Bob,user

encoded, _ := gotoon.Encode(data,
    gotoon.WithIndent(4),
    gotoon.WithDelimiter("\t"),
    gotoon.WithLengthMarker(),
)

Simple objects with primitive values:

data := map[string]interface{}{
    "id":     123,
    "name":   "Ada",
    "active": true,
}
// Output:
// id: 123
// name: Ada
// active: true

Nested objects:

data := map[string]interface{}{
    "user": map[string]interface{}{
        "id":   123,
        "name": "Ada",
    },
}
// Output:
// user:
//   id: 123
//   name: Ada

data := map[string]interface{}{
    "tags": []string{"admin", "ops", "dev"},
}
// Output:
// tags[3]: admin,ops,dev

When all objects share the same primitive fields, TOON uses an efficient tabular format:

data := map[string]interface{}{
    "items": []map[string]interface{}{
        {"sku": "A1", "qty": 2, "price": 9.99},
        {"sku": "B2", "qty": 1, "price": 14.5},
    },
}
// Output:
// items[2]{price,qty,sku}:
//   9.99,2,A1
//   14.5,1,B2

Arrays that don't meet tabular requirements use list format:

data := map[string]interface{}{
    "items": []interface{}{
        1,
        "text",
        map[string]interface{}{"key": "value"},
    },
}
// Output:
// items[3]:
//   - 1
//   - text
//   - key: value

TOON quotes strings only when necessary to maximize token efficiency:

• Empty strings: ""
• Contains delimiter, colon, quotes, or control chars: "hello, world"
• Leading/trailing spaces: " padded "
• Looks like boolean/number/null: "true", "42"
• Unicode and emoji are safe unquoted: hello 👋 world

See the examples/basic directory for more comprehensive examples including:

• Simple objects
• Tabular arrays
• Nested structures
• Primitive arrays
• Using structs with JSON tags
• Custom delimiters
• Mixed arrays
• Time values
• E-commerce orders

Run the examples:

cd examples/basic
go run main.go

go test -v

Based on the original TOON benchmarks using GPT-5's tokenizer:

• GitHub Repositories (100 repos): 42.3% token reduction vs JSON
• Daily Analytics (180 days): 58.9% token reduction vs JSON
• E-Commerce Order: 35.4% token reduction vs JSON

Overall: 49.1% token reduction vs JSON across all benchmarks

JSON (257 tokens):

{
  "order": {
    "id": "ORD-12345",
    "customer": {
      "name": "John Doe",
      "email": "john@example.com"
    },
    "items": [
      { "sku": "WIDGET-1", "quantity": 2, "price": 19.99 },
      { "sku": "GADGET-2", "quantity": 1, "price": 49.99 }
    ],
    "total": 89.97
  }
}

TOON (166 tokens - 35.4% reduction):

order:
  customer:
    email: john@example.com
    name: John Doe
  id: ORD-12345
  items[2]{price,quantity,sku}:
    19.99,2,WIDGET-1
    49.99,1,GADGET-2
  total: 89.97

gotoon/
├── go.mod              # Go module definition
├── README.md           # This file
├── toon.go             # Public API (Encode function)
├── types.go            # Options and type definitions
├── constants.go        # String constants and delimiters
├── normalize.go        # Value normalization and type guards
├── writer.go           # LineWriter implementation
├── primitives.go       # Primitive encoding and quoting
├── encoders.go         # Core encoding logic
├── toon_test.go        # Unit tests
└── examples/
    └── basic/
        └── main.go     # Example usage

• Deterministic output: Map keys are sorted alphabetically for consistent encoding
• Reflection-based normalization: Automatically converts structs, slices, and maps
• Efficient string building: Uses strings.Builder for performance
• Type-safe options: Functional options pattern for clean API
• Comprehensive testing: Full test coverage with table-driven tests

TOON works best when you show the format instead of describing it. The structure is self-documenting – models parse it naturally once they see the pattern.

Wrap your encoded data in a fenced code block:

```toon
users[3]{id,name,role}:
  1,Alice,admin
  2,Bob,user
  3,Charlie,user
```

For output, be more explicit:

Data is in TOON format (2-space indent, arrays show length and fields).

Task: Return only users with role "user" as TOON. Use the same header.
Set [N] to match the row count. Output only the code block.

GoTOON is a Go port of the original TOON format created by Johann Schopplich.