About json2toon.co
An independent, free JSON to TOON converter for people who send structured data to LLMs.
What we build
json2toon.co started in November 2025 as a simple way to paste JSON and see it as TOON, the token-oriented format designed to make structured data cheaper to put in an LLM prompt. It has since grown into a small toolkit: conversion between JSON, TOON, TONL, CSV, YAML, XML, TOML and Protobuf, JSON repair, JSONPath queries, JSON Schema validation, a JWT decoder, batch conversion, a free public API and a Chrome extension.
The web app is free, needs no account, and runs its conversions in your browser, so the data you paste stays on your device. The code is on GitHub.
Relationship to the TOON project
json2toon.co is an independent project. We did not create the TOON format and we are not affiliated with its authors. The converter uses the official open-source @toon-format/toon library for TOON and the tonl package for TONL, so the output follows those projects' specifications rather than our own variant.
Where our numbers come from
When we say TOON uses about 40% fewer tokens than JSON, we mean the result of the official TOON benchmark: 39.9% fewer tokens on average across 5,016 LLM calls on four models, ranging from about 22% on mixed, nested data to about 59% on uniform tables. We break this down in our benchmark write-up. Your own savings depend on the shape of your data, which is why the converter shows the token counts for your actual input. We also publish when not to use TOON.
How we write the blog
- Articles are published by the json2toon.co maintainers.
- Statistics should come from a named source (benchmark, documentation or paper), linked in the article.
- If you spot an error, tell us. We fix factual errors and update the article's modified date.
Contact
Bug reports, feature requests and corrections go through GitHub. See the contact page.