TOON Validator + Linter + Converter

The TOON Developer Toolkit

Validate TOON syntax, catch errors, and convert between JSON and TOON format. Free, instant, runs in your browser.

Lint
Validate TOON
↔
JSON ↔ TOON
60%
Token reduction
100%
Private
Load example
TOON Input
Results — paste TOON to begin
Paste TOON on the left to validate.

ToonLint checks for:
• Correct header syntax
• Column count matches
• Indentation consistency
• Valid primitive values
• Structural completeness
Examples
JSON Input
TOON Output
// Output appears here...

TOON Format Reference

TOON (Token-Oriented Object Notation) is a compact, human-readable encoding designed for LLM prompts. It reduces token usage by 30–60% compared to JSON.

Syntax Rules

✓ Uniform array of objects
key[N]{f1,f2,f3}:
One data row per object, comma-separated values
✓ Simple array
key[N]: v1,v2,v3
All values on one line after the colon
✓ Nested object
key:
Children indented by 2 spaces on next lines
✓ Primitive value
key: value
No quotes unless value contains comma or colon

ToonLint Error Codes

E001 Invalid header
Array header must match key[N]{fields}: or key[N]: values
E002 Column mismatch
Data row has different number of values than declared fields
E003 Row count mismatch
Actual data rows don't match the declared [N] count
W001 Inconsistent indent
Indentation is not a multiple of 2 spaces

FAQ

What is ToonLint?
ToonLint is a free online validator and linter for TOON (Token-Oriented Object Notation) format. It checks your TOON syntax for errors and warnings, and also converts between JSON and TOON.
What is TOON format?
TOON is a compact, human-readable encoding of JSON designed for LLM prompts. It reduces token usage by 30–60% by using a tabular format for arrays and minimal syntax for objects.
Is my data private?
100%. All validation and conversion runs entirely in your browser. No data is ever sent to any server.
Which LLMs support TOON?
All major LLMs — GPT-4, Claude, Gemini, Llama. Since TOON is plain text, no special training is needed.