JSON Schema in TOON Format

[woutervancgi]

When TOON would fully implement JSON Schema we can make TOON DRY; repeating items can be implemented once and used as reference, this makes TOON even more compact.

Current implementation

Pattern	TOON vs YAML	Reason
Reused schemas	🔴 20-30x larger	No anchors/aliases - must inline everything
allOf with base schemas	🔴 2-3x larger	Base schema copied multiple times
Error responses	🔴 30x larger	Same error schema repeated ~30 times
Nested object properties	🔴 2-5x larger	Cannot use references
Deeply nested structures	🔴 3-4x larger	All nesting must be explicit
Primitive enums	✅ ~10% smaller	Inline format wins
Tabular arrays	✅ 40-60% smaller	(But only if no nested objects!)

Proposal to address these

As JSON is widely in use and mature as Object Notation format, using all the lessons learned form JSON in TOON can help maturing it quickly.
So to help in this transition and the implementation process I have converted JSON Schema Draft 2020-12 into TOON with the help of Claude Sonnet 4.5.

json-schema-toon-spec.toon.txt
json-schema-toon-spec.html
json-schema-toon-spec.md

I have run multiple tests, please review it as well.
Let me know if you endorse this approach and like to move this way forward.

[johannschopplich]

@woutervancgi Love the idea so far, as making TOON more mature is a key priority! Thanks for the examples provided.

Would you mind creating an RFC in the spec repo? We first would have to define the scope and changes, define conformance tests, before moving on to any implementation.

[DoiiarX]

@johannschopplich
Modern tools like Ollama seem to be able to use JSON Schema to constrain the sampler that predicts the next token, discarding tokens that do not conform to the rules, thereby achieving 100% accurate JSON output. If Toon were to integrate into this ecosystem, allowing the model not only to understand the Toon format but also to output perfect Toon format, that would be excellent.

ollama/ollama#7900

[BrickDesignerNL]

@johannschopplich I will tomorrow, thanks.

@DoiiarX even stronger: small model versions of for example Qwen3-0528 you can just give a JSON Schema - or more powerful: you can let it create a JSON Schema - and when provided correctly, the model itself, regardless of if you use Ollama or not, will comply it's output to the schema.

So if TOON becomes JSON Schema compliant, transforming between JSON, YAML and TOON is just a 1:1 (except for comments in yaml). So very powerful.

I've also created an OpenAPI v3.2 spec in TOON based on the attached above,, but let's firstindeed as @johannschopplich says make the TOON spec solid.

[horeraabu66-boop]

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[hermanndelcampo-theaiqueen]

I already created some PR for this.

#126

I am happy to get feedback after testing.

[woutervancgi]

@woutervancgi Love the idea so far, as making TOON more mature is a key priority! Thanks for the examples provided.

Would you mind creating an RFC in the spec repo? We first would have to define the scope and changes, define conformance tests, before moving on to any implementation.

toon-format/spec#7

Sorry a very long RFC text.
Added example change for SPEC.md to it as well, based on the existing one instead of the one created from scratch.