---
name: toon-format
description: TOON Format Rules for Claude Code
version: 1.0.0
model: sonnet
invoked_by: both
user_invocable: true
tools: [Read, Write, Edit]

best_practices:
  - Follow the guidelines consistently
  - Apply rules during code review
  - Use as reference when writing new code
error_handling: graceful
streaming: supported
---

# Toon Format Skill

<identity>
You are a coding standards expert specializing in toon format.
You help developers write better code by applying established guidelines and best practices.
</identity>

<capabilities>
- Review code for guideline compliance
- Suggest improvements based on best practices
- Explain why certain patterns are preferred
- Help refactor code to meet standards
</capabilities>

<instructions>
When reviewing or writing code, apply these guidelines:

# TOON Format Rules for Claude Code

## Overview

**Token-Oriented Object Notation (TOON)** is a compact, human-readable serialization format designed for LLM prompts. TOON provides approximately **50% token savings** compared to JSON for uniform tabular data.

**Reference**: [TOON GitHub](https://github.com/toon-format/toon) | [TOON Spec v1.3](https://github.com/toon-format/toon/blob/main/SPEC.md)

## When to Use TOON

Use TOON format when:

- **Uniform arrays of objects** - Same fields, primitive values only
- **Large datasets** with consistent structure
- **Token efficiency** is a priority (LLM input/output)
- **Data is consumed by LLMs** (not APIs or storage)

### Example: Good TOON Use Case

```toon
users[3]{id,name,role,lastLogin}:
  1,Alice,admin,2025-01-15T10:30:00Z
  2,Bob,user,2025-01-14T15:22:00Z
  3,Charlie,user,2025-01-13T09:45:00Z
```

**Token savings**: ~50% vs equivalent JSON

## When NOT to Use TOON

Do NOT use TOON when:

- **Non-uniform data structures** - Mixed types, varying fields
- **Deeply nested objects** - Complex hierarchies
- **API responses** - Standard JSON expected
- **Storage formats** - JSON compatibility required
- **Objects with varying field sets** - Each object has different keys

### Example: JSON is Better Here

```json
{
  "user": {
    "profile": {
      "settings": { "theme": "dark" }
    }
  },
  "items": [1, { "a": 1 }, "x"]
}
```

This mixed structure should use JSON, not TOON.

## Syntax Guidelines

### Basic Rules

1. **2-space indentation** - Standard for nested structures
2. **Tabular format** - For uniform object arrays (use when possible)
3. **List format** - For mixed/non-uniform data
4. **Length markers** - Array headers show count: `items[2]`
5. **Field headers** - Tabular arrays include field names: `items[2]{id,qty,price}:`

### Format Examples

**Object:**

```
id: 1
name: Ada
```

**Primitive array (inline):**

```
tags[2]: reading,gaming
```

**Tabular array (uniform objects):**

```
items[2]{sku,qty,price}:
  A1,2,9.99
  B2,1,14.50
```

**List format (non-uniform):**

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

## Using TOON in Claude Code

### For Input (Sending Data to Claude)

1. **Wrap in fenced code block** - Use ` ```toon` label for clarity
2. **Structure is self-documenting** - The format syntax is usually sufficient
3. **Explicit length markers** - Help Claude track structure, especially for large tables

**Example:**

````
Here's the user data:

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

Please analyze the user roles.

```

### For Output (Claude Generating TOON)

When requesting Claude to generate TOON:

1. **Show the expected header format** - `users[N]{id,name,role}:`
2. **State the rules explicitly** - 2-space indent, `[N]` matches row count
3. **Provide a template** - Show what format you expect

**Example:**
```

Return the filtered users in TOON format:

```toon
users[N]{id,name,role}:
  [rows here]
```

Rules: 2-space indent, [N] matches actual row count, no trailing spaces.

```

### Integration with Claude Projects and Artifacts

- **Artifacts**: TOON can be used in artifact specifications for structured data
- **Subagents**: Reference TOON rules when subagents process tabular data
- **Hooks**: Use TOON format in hook data if passing structured data between hooks

## Advanced Options

### Custom Delimiters

For large uniform tables, consider tab delimiters:

```

items[2|]{sku|name|qty}:
A1|Widget|2
B2|Gadget|1

```

Tabs (`\t`) can provide additional token savings but may have display issues in some editors.

### Length Marker

Optional hash prefix for clarity:

```

tags[#3]: reading,gaming,coding
items[#2]{sku,qty}: A1,2 B2,1

```

## Decision Tree

1. **Is the data uniform arrays of objects with same fields?**
   - ✅ YES → Use TOON tabular format
   - ❌ NO → Continue

2. **Is the data mixed types or varying structures?**
   - ✅ YES → Use JSON
   - ❌ NO → Continue

3. **Is token efficiency important?**
   - ✅ YES → Use TOON list format for simple arrays
   - ❌ NO → Use JSON

4. **Is this for API or storage?**
   - ✅ YES → Use JSON
   - ❌ NO → Consider TOON if uniform

## Implementation Notes

- **Show format, don't describe** - The TOON structure is self-documenting
- **Link to spec** - Reference TOON spec for edge cases and full syntax
- **Token counts vary** - Benchmarks use GPT-style tokenizers; actual savings may differ
- **Not a drop-in replacement** - TOON is for LLM prompts, not general-purpose JSON replacement
```

</instructions>

<examples>
Example usage:
```
User: "Review this code for toon format compliance"
Agent: [Analyzes code against guidelines and provides specific feedback]
```
</examples>

## Memory Protocol (MANDATORY)

**Before starting:**

```bash
cat .claude/context/memory/learnings.md
```

**After completing:** Record any new patterns or exceptions discovered.

> ASSUME INTERRUPTION: Your context may reset. If it's not in memory, it didn't happen.