TOON
toon-format
Token-Oriented Object Notation - a compact serialization format that uses ~40% fewer tokens than JSON.
What is TOON?
TOON is a serialization format and multi-language SDK (TS, Python, Go, Rust, .NET, Java, Swift) for sending uniform arrays to LLMs more token-efficiently than JSON. It ships a formal spec, CLI, VS Code extension, Tree-sitter grammar and online playground, and claims 76% accuracy at ~40% fewer tokens versus JSON across 5,016 evaluations (project's own claim).
Pros & Cons
Pros
- Format-level token savings are model-agnostic - works with any LLM, no SDK or proxy required
- Seven-language SDK and a VS Code extension lower the adoption barrier
- Formal spec and Tree-sitter grammar signal a durable, toolable standard
Cons
- Only efficient for uniform arrays of objects - nested/irregular JSON sees no benefit
- Very high star count for a data-format library warrants watching
- Adoption requires buy-in from both producer and consumer of the data
License
MIT (OSI-open)
When it is interesting
Feeding large tabular datasets (search results, DB rows, catalogs) into prompts where JSON verbosity is a measurable cost.
When it is too early
If your payloads are mostly free-text, nested config or irregular structures.
This repo featured in the 2026-07 edition of the Open-Source AI Radar.
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