JSON to TOON Converter: Cut LLM Tokens ~43% | json2toon

Convert JSON to TOON in one click and cut LLM prompt tokens. Live token counter and right-click conversion. Runs locally.

Convert JSON to TOON in one click and send the same data to your AI assistant with far fewer tokens. json2toon runs the conversion right in your browser, shows the exact token savings, and copies the result to your clipboard. Nothing is uploaded. WHAT IS TOON? TOON (Token-Oriented Object Notation) is a compact, human-readable data format designed for large language model (LLM) prompts. It writes the keys of a uniform array once, as a header, and then lists each item as a row, instead of repeating every key and quote like JSON does. In the official TOON benchmark (v4.1, 5,856 LLM calls), TOON used about 43% fewer tokens than JSON on average, with equal or slightly better answer accuracy (72.2% vs 71.4%). Flat tables save the most (around 59%); deeply nested data saves less (around 33%). Example. This JSON: {"users":[{"id":1,"name":"Alice","role":"admin"},{"id":2,"name":"Bob","role":"user"}]} becomes this TOON: users[2]{id,name,role}: 1,Alice,admin 2,Bob,user WHAT THE EXTENSION DOES • Popup converter: click the toolbar icon or press Alt+Shift+J, paste your data, and the TOON output updates as you type. • Live token counter: input and output token counts with the GPT-4o tokenizer, plus the percentage saved. • Right-click any selection: select JSON on a web page and choose json2toon → Convert to TOON. The result is copied to your clipboard and a small notice shows the token savings. • Other formats too: paste YAML, CSV or XML instead of JSON. The input format is detected automatically, and you can convert TOON back to JSON. • Options: indent size and delimiter. • JSON repair: fixes common JSON errors such as trailing commas and single quotes. • Built-in examples to try it in seconds. • Open in editor: send your data to the full json2toon.co editor for more tools. WHO IT IS FOR • Developers building LLM apps, agents and RAG pipelines who pass JSON tool results or API responses into prompts. • Anyone pasting tables, logs or API data into a chat assistant who wants to stay under the context window and pay less per request. • Prompt engineers comparing token counts across formats. PRIVACY All conversion runs locally inside the extension. Your data never leaves your browser: there is no server, no analytics and no account. The extension only touches a page when you right-click a selection and choose a json2toon action. It is free and open source: https://github.com/karta9821/json2toon FAQ Does TOON work with ChatGPT and Claude? Yes. TOON is plain text, so any LLM can read it. Paste it into the prompt like you would paste JSON. How many tokens will I save? It depends on the shape of your data. Uniform arrays of objects, such as tables and logs, usually save 40 to 60%. The extension shows the exact count for your input before you copy it. Is TOON lossless? Yes. TOON encodes the same data model as JSON, and you can convert it back to JSON with this extension. When should I not use TOON? For deeply nested or irregular data the savings are smaller, and plain JSON may be just as compact. The token counter shows you which is smaller. Website and full editor: https://json2toon.co TOON format docs: https://json2toon.co/docs/toon