⚡ What is ToonLint?
ToonLint is a free, browser-based developer tool for working with TOON (Token-Oriented Object Notation) format. It provides three core tools in one place: a TOON linter/validator, a JSON-to-TOON converter, and a TOON-to-JSON converter.
TOON is a compact, human-readable data format specifically designed for LLM prompts. By converting JSON to TOON, developers can reduce token usage by 30–60%, directly lowering API costs when working with GPT-4, Claude, Gemini, and other large language models.
ToonLint was built because TOON is new — developers needed a reliable way to validate their TOON syntax and catch errors before sending data to expensive LLM APIs.
🛠️ Our Tools
TOON Validator & Linter
Paste any TOON document and instantly validate its syntax. ToonLint checks for header format errors (E001), column count mismatches (E002), row count mismatches (E003), and indentation warnings (W001). Each error includes a suggested fix.
JSON → TOON Converter
Paste any valid JSON and convert it to TOON format instantly. Uniform arrays of objects are converted to the efficient tabular format. Shows exact token savings compared to JSON.
TOON → JSON Converter
Convert TOON back to standard JSON format. Fully lossless — supports tabular arrays, nested objects, simple arrays, and all primitive types.
🔒 Privacy First
100% Browser-Based
All validation and conversion runs entirely in your browser using JavaScript. Nothing is sent to any server.
No Data Collection
We don't store, log, or transmit your JSON or TOON data. Your sensitive API responses stay on your device.
No Account Required
No sign-up, no login, no email. Open the tool and start using it immediately.
⚠️ Disclaimer
ToonLint is an independent developer tool and is not affiliated with the official TOON specification or the toon-format organization. TOON is an emerging format and the specification may evolve. Always refer to the official TOON specification for the authoritative format definition. Token savings estimates are approximations based on character count and may vary by model and tokenizer.
✉️ Contact
Get in Touch
Found a bug? Have a feature request? Want to report incorrect TOON validation behavior? We'd love to hear from you.
hello@toonlint.dev