toon/docs/cli/index.md

Command Line Interface

The @toon-format/cli package provides a command-line interface for encoding JSON to TOON and decoding TOON back to JSON. Use it for quick conversions without writing code, estimating token savings before sending data to LLMs, or integrating TOON into shell pipelines with tools like curl and jq. It supports stdin/stdout workflows, multiple delimiter options, token statistics, and all encoding/decoding features available in the library.

The CLI is built on top of the @toon-format/toon TypeScript implementation and adheres to the latest specification.

Usage

Without Installation

Use npx to run the CLI without installing:

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npx @toon-format/cli input.json -o output.toon

npx @toon-format/cli data.toon -o output.json

echo '{"name": "Ada"}' | npx @toon-format/cli

:::

Global Installation

Or install globally for repeated use:

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npm install -g @toon-format/cli

pnpm add -g @toon-format/cli

yarn global add @toon-format/cli

:::

After global installation, use the toon command:

toon input.json -o output.toon

Basic Usage

Auto-Detection

The CLI automatically detects the operation based on file extension:

• .json files → encode (JSON to TOON)
• .toon files → decode (TOON to JSON)

When reading from stdin, use --encode or --decode flags to specify the operation (defaults to encode).

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toon input.json -o output.toon

toon data.toon -o output.json

toon input.json

cat data.json | toon
echo '{"name": "Ada"}' | toon

cat data.toon | toon --decode

:::

Standard Input

Omit the input argument or use - to read from stdin. This enables piping data directly from other commands:

# No argument needed
cat data.json | toon

# Explicit stdin with hyphen (equivalent)
cat data.json | toon -

# Decode from stdin
cat data.toon | toon --decode

Options

Option	Description
-o, --output <file>	Output file path (prints to stdout if omitted)
-e, --encode	Force encode mode (overrides auto-detection)
-d, --decode	Force decode mode (overrides auto-detection)
--delimiter <char>	Array delimiter: , (comma), \t (tab), | (pipe)
--indent <number>	Indentation size (default: 2)
--stats	Show token count estimates and savings (encode only)
--no-strict	Disable strict validation when decoding
--key-folding <mode>	Key folding mode: off, safe (default: off)
--flatten-depth <number>	Maximum segments to fold (default: Infinity) – requires --key-folding safe
--expand-paths <mode>	Path expansion mode: off, safe (default: off)

Advanced Examples

Token Statistics

Show token savings when encoding:

toon data.json --stats -o output.toon

This helps you estimate token cost savings before sending data to LLMs.

Alternative Delimiters

TOON supports three delimiters: comma (default), tab, and pipe. Alternative delimiters can provide additional token savings in specific contexts.

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toon data.json --delimiter "\t" -o output.toon

toon data.json --delimiter "|" -o output.toon

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Tab delimiter example:

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items[2	]{id	name	qty	price}:
  A1	Widget	2	9.99
  B2	Gadget	1	14.5

items[2]{id,name,qty,price}:
  A1,Widget,2,9.99
  B2,Gadget,1,14.5

:::

Tip

Tab delimiters often tokenize more efficiently than commas and reduce the need for quote-escaping. Use --delimiter "\t" for maximum token savings on large tabular data.

Lenient Decoding

Skip validation for faster processing:

toon data.toon --no-strict -o output.json

Lenient mode (--no-strict) disables strict validation checks like array count matching, indentation multiples, and delimiter consistency. Use this when you trust the input and want faster decoding.

Stdin Workflows

The CLI integrates seamlessly with Unix pipes and other command-line tools:

# Convert API response to TOON
curl https://api.example.com/data | toon --stats

# Process large dataset
cat large-dataset.json | toon --delimiter "\t" > output.toon

# Chain with jq
jq '.results' data.json | toon > filtered.toon

Key Folding

Collapse nested wrapper chains to reduce tokens (since spec v1.5):

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toon input.json --key-folding safe -o output.toon

toon input.json --key-folding safe --flatten-depth 2 -o output.toon

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Example:

For data like:

{
  "data": {
    "metadata": {
      "items": ["a", "b"]
    }
  }
}

With --key-folding safe, output becomes:

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

Instead of:

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

Path Expansion

Reconstruct nested structure from folded keys when decoding:

toon data.toon --expand-paths safe -o output.json

This pairs with --key-folding safe for lossless round-trips.

Round-Trip Workflow

# Encode with folding
toon input.json --key-folding safe -o compressed.toon

# Decode with expansion (restores original structure)
toon compressed.toon --expand-paths safe -o output.json

# Verify round-trip
diff input.json output.json

Combined Options

Combine multiple options for maximum efficiency:

# Key folding + tab delimiter + stats
toon data.json --key-folding safe --delimiter "\t" --stats -o output.toon