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240 lines
7.2 KiB
Markdown
240 lines
7.2 KiB
Markdown
# Getting Started
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## What is TOON?
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**Token-Oriented Object Notation** is a compact, human-readable encoding of the JSON data model that minimizes tokens and makes structure easy for models to follow. It's intended for *LLM input* as a lossless, drop-in representation of JSON data.
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TOON combines YAML's indentation-based structure for nested objects with a CSV-style tabular layout for uniform arrays. TOON's sweet spot is uniform arrays of objects (multiple fields per row, same structure across items), achieving CSV-like compactness while adding explicit structure that helps LLMs parse and validate data reliably.
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Think of it as a translation layer: use JSON programmatically, and encode it as TOON for LLM input.
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### Why TOON?
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Standard JSON is verbose and token-expensive. For uniform arrays of objects, JSON repeats every field name for every record:
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```json
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{
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"users": [
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{ "id": 1, "name": "Alice", "role": "admin" },
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{ "id": 2, "name": "Bob", "role": "user" }
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]
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}
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```
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YAML already reduces some redundancy with indentation instead of braces:
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```yaml
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users:
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- id: 1
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name: Alice
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role: admin
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- id: 2
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name: Bob
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role: user
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```
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TOON goes further by declaring fields once and streaming data as rows:
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```yaml
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users[2]{id,name,role}:
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1,Alice,admin
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2,Bob,user
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```
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The `[2]` declares the array length, enabling LLMs to answer dataset size questions and detect truncation. The `{id,name,role}` declares the field names. Each row is then a compact, comma-separated list of values. This is the core pattern: declare structure once, stream data compactly. The format approaches CSV's efficiency while adding explicit structure.
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For a more realistic example, here's how TOON handles a dataset with both nested objects and tabular arrays:
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::: code-group
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```json [JSON (235 tokens)]
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{
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"context": {
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"task": "Our favorite hikes together",
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"location": "Boulder",
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"season": "spring_2025"
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},
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"friends": ["ana", "luis", "sam"],
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"hikes": [
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{
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"id": 1,
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"name": "Blue Lake Trail",
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"distanceKm": 7.5,
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"elevationGain": 320,
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"companion": "ana",
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"wasSunny": true
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},
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{
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"id": 2,
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"name": "Ridge Overlook",
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"distanceKm": 9.2,
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"elevationGain": 540,
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"companion": "luis",
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"wasSunny": false
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},
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{
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"id": 3,
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"name": "Wildflower Loop",
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"distanceKm": 5.1,
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"elevationGain": 180,
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"companion": "sam",
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"wasSunny": true
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}
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]
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}
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```
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```yaml [TOON (106 tokens)]
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context:
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task: Our favorite hikes together
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location: Boulder
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season: spring_2025
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friends[3]: ana,luis,sam
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hikes[3]{id,name,distanceKm,elevationGain,companion,wasSunny}:
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1,Blue Lake Trail,7.5,320,ana,true
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2,Ridge Overlook,9.2,540,luis,false
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3,Wildflower Loop,5.1,180,sam,true
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```
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:::
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Notice how TOON combines YAML's indentation for the `context` object with inline format for the primitive `friends` array and tabular format for the structured `hikes` array. Each format is chosen automatically based on the data structure.
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### Design Goals
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TOON is optimized for specific use cases. It aims to:
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- Make uniform arrays of objects as compact as possible by declaring structure once and streaming data.
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- Stay fully lossless and deterministic – round-trips preserve all data and structure.
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- Keep parsing simple and robust for both LLMs and humans through explicit structure markers.
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- Provide validation guardrails (array lengths, field counts) that help detect truncation and malformed output.
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## When to Use TOON
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TOON excels with uniform arrays of objects – data with the same structure across items. For LLM prompts, the format produces deterministic, minimally quoted text with built-in validation. Explicit array lengths (`[N]`) and field headers (`{fields}`) help detect truncation and malformed data, while the tabular structure declares fields once rather than repeating them in every row.
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::: tip
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The TOON format is stable, but also an idea in progress. Nothing's set in stone – help shape where it goes by contributing to the [spec](https://github.com/toon-format/spec) or sharing feedback.
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:::
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## When Not to Use TOON
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TOON is not always the best choice. Consider alternatives when:
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- **Deeply nested or non-uniform structures** (tabular eligibility ≈ 0%): JSON-compact often uses fewer tokens. Example: complex configuration objects with many nested levels.
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- **Semi-uniform arrays** (~40–60% tabular eligibility): Token savings diminish. Prefer JSON if your pipelines already rely on it.
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- **Pure tabular data**: CSV is smaller than TOON for flat tables. TOON adds minimal overhead (~5-10%) to provide structure (array length declarations, field headers, delimiter scoping) that improves LLM reliability.
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- **Latency-critical applications**: Benchmark on your exact setup. Some deployments (especially local/quantized models) may process compact JSON faster despite TOON's lower token count.
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> [!NOTE]
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> For data-driven comparisons across different structures, see [benchmarks](/guide/benchmarks). When optimizing for latency, measure TTFT, tokens/sec, and total time for both TOON and JSON-compact and use whichever performs better in your specific environment.
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## Installation
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### TypeScript Library
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Install the library via your preferred package manager:
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::: code-group
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```bash [npm]
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npm install @toon-format/toon
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```
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```bash [pnpm]
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pnpm add @toon-format/toon
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```
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```bash [yarn]
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yarn add @toon-format/toon
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```
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:::
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### CLI
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The CLI can be used without installation via `npx`, or installed globally:
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::: code-group
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```bash [npx (no install)]
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npx @toon-format/cli input.json -o output.toon
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```
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```bash [npm]
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npm install -g @toon-format/cli
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```
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```bash [pnpm]
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pnpm add -g @toon-format/cli
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```
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```bash [yarn]
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yarn global add @toon-format/cli
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```
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:::
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For full CLI documentation, see the [CLI reference](/cli/).
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## Your First Example
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The examples below use the TypeScript library for demonstration, but the same operations work in any language with a TOON implementation.
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Let's encode a simple dataset with the TypeScript library:
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```ts
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import { encode } from '@toon-format/toon'
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const data = {
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users: [
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{ id: 1, name: 'Alice', role: 'admin' },
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{ id: 2, name: 'Bob', role: 'user' }
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]
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}
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console.log(encode(data))
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```
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**Output:**
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```yaml
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users[2]{id,name,role}:
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1,Alice,admin
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2,Bob,user
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```
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### Decoding Back to JSON
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Decoding is just as simple:
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```ts
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import { decode } from '@toon-format/toon'
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const toon = `
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users[2]{id,name,role}:
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1,Alice,admin
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2,Bob,user
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`
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const data = decode(toon)
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console.log(JSON.stringify(data, null, 2))
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```
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**Output:**
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```json
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{
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"users": [
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{ "id": 1, "name": "Alice", "role": "admin" },
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{ "id": 2, "name": "Bob", "role": "user" }
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]
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}
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```
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Round-tripping is lossless: `decode(encode(x))` always equals `x` (after normalization of non-JSON types like `Date`, `NaN`, etc.).
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## Where to Go Next
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Now that you've seen your first TOON document, read the [Format Overview](/guide/format-overview) for complete syntax details (objects, arrays, quoting rules, key folding), then explore [Using TOON with LLMs](/guide/llm-prompts) to see how to use it effectively in prompts. For implementation details, check the [API reference](/reference/api) (TypeScript) or the [specification](/reference/spec) (language-agnostic normative rules).
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