TOON API

What it does

The endpoint parses your input and encodes it as TOON with the official @toon-format/toon library. TOON uses about 43% fewer tokens than JSON on average (42.6% in the official TOON v4.1 benchmark), so it is a cheap way to shrink LLM prompts from a backend, a script or a no-code tool that can make HTTP calls.

POST https://json2toon.co/api/v1/toon

Request body (JSON):

• content (string, required): the raw input. Objects must be stringified first.
• format (optional): json, yaml, toml or xml. If omitted, the API tries JSON, YAML, TOML, then XML.
• options (optional): passed to the TOON encoder, e.g. {"delimiter": "|", "indentSize": 4}.

Try it

This form sends a real request to the API from your browser.

Examples

curl

curl -X POST https://json2toon.co/api/v1/toon \
  -H "Content-Type: application/json" \
  -d '{"content": "{\"users\":[{\"id\":1,\"name\":\"Ann\"},{\"id\":2,\"name\":\"Bob\"}]}", "format": "json"}'

JavaScript (fetch)

const data = { users: [{ id: 1, name: "Ann" }, { id: 2, name: "Bob" }] }

const res = await fetch("https://json2toon.co/api/v1/toon", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  // content must be a string, so stringify your object first
  body: JSON.stringify({ content: JSON.stringify(data), format: "json" }),
})
if (!res.ok) throw new Error((await res.json()).error)
const toon = await res.text()

Python (requests)

import json, requests

data = {"users": [{"id": 1, "name": "Ann"}, {"id": 2, "name": "Bob"}]}
res = requests.post(
    "https://json2toon.co/api/v1/toon",
    json={"content": json.dumps(data), "format": "json"},
)
res.raise_for_status()
toon = res.text

Response format

On success the API returns 200 with the TOON document as plain text (not JSON). For the examples above:

users[2]{id,name}:
  1,Ann
  2,Bob

If you leave out format, the response also carries an X-Performance-Warning header suggesting you set it.

Errors

Errors come back as JSON with a single error field:

Limits

No API key and no rate limit at the moment. It is a free service with no uptime guarantee, and it only converts to TOON (not back). Your data is processed on our server in memory and not stored; see the privacy policy. The full OpenAPI reference is in the API docs.

API or library?

If your code runs in JavaScript or TypeScript, installing @toon-format/toon is usually better: no network round trip, no dependency on our uptime, it works offline, your data never leaves your machine, and you also get decode(). See the TypeScript install guide or the other languages.

The API is handy when you cannot add a dependency: shell scripts, no-code tools like Zapier or n8n, languages without a TOON library yet, or a quick test before you commit to the format.

Using an AI assistant? Try the MCP server

If you want ChatGPT, Claude, Cursor or VS Code to do the conversion, connect the TOON MCP server instead. It exposes json_to_toon and toon_to_json tools, so it also decodes. To see how many tokens you would save first, paste a sample into the TOON token calculator.

FAQ