Idir Ouhab Meskine
November 11, 2025
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If you're building AI applications, you've probably noticed that token costs add up fast. Every API call counts, and the format you use to structure data matters more than you think.
Enter TOON (Token-Oriented Object Notation), a format designed specifically for LLM contexts. Let's see how it stacks up against JSON and what you can actually save.
TOON is a lightweight data serialization format optimized for token efficiency. Instead of the verbose syntax of JSON, TOON uses a more compact representation that LLMs can still parse easily.
JSON Example:
json{ "name": "John Smith", "age": 32, "email": "[email protected]", "active": true }
TOON Example:
toonname: John Smith age: 32 email: [email protected] active: true
Simple difference, but it matters at scale.
Let's look at real numbers. Using GPT-4's tokenizer:
JSON format (95 characters):
{, }, ", ,, extra spacingTOON format (73 characters):
Savings: 25% fewer tokens per object
When you're working with arrays and nested objects, the savings multiply:
JSON (62 tokens):
json{ "users": [ { "id": 1, "name": "Alice", "roles": ["admin", "editor"] }, { "id": 2, "name": "Bob", "roles": ["viewer"] } ] }
TOON (43 tokens):
toonusers: items[2]: - id: 1 name: Alice roles: items[2]: - admin - editor - id: 2 name: Bob roles: items[1]: - viewer
Savings: 29% reduction in tokens
If you're feeding API responses into your prompts, this adds up quickly. A typical API response with 10 objects:
At $10 per million tokens (GPT-4 pricing), processing 10,000 requests:
Perfect for:
Stick with JSON when:
Let's say you're building a RAG system that processes 1,000 documents daily, each with metadata in your prompt:
Daily token usage:
Monthly difference:
For a single application. Multiply this across multiple workflows, and you're looking at meaningful cost reduction.
TOON isn't revolutionary, but it's practical. If you're watching token budgets (and you should be), switching internal data formats from JSON to TOON can cut costs by 25-35% without changing functionality.
The format is readable, LLMs handle it naturally, and the savings compound over time.
Worth testing in your next project. Tool to convert JSON a TOON
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