I Replaced JSON with TOON in My LLM Prompts and Saved 40% on Tokens. Here's How published: false

Hey! I'm Andrey, a frontend developer at Cloud.ru , and I write about frontend and AI on my blog and Telegram channel . I work with LLM APIs every day. And every day I send structured data into context: product lists, logs, users, metrics. All of it - JSON. All of it - money. At some point I calculated how many tokens in my prompts go to curly braces, quotes, and repeated keys. Turns out - a lot. Way too much. Then I tried TOON. Here's what happened. The Problem: JSON Is a Generous Format Take a typical case. You're building a RAG system or an AI assistant that analyzes data. Your prompt pulls in a list of 50 records. Here's one record in JSON: { "id" : 2001 , "timestamp" : "2025-11-18T08:14:23Z" , "level" : "error" , "service" : "auth-api" , "ip" : "172.16.4.21" , "message" : "Auth failed for user" , "code" : "AUTH_401" } Now multiply by 50. Each record repeats 7 keys: "id" , "timestamp" , "level" , "service" , "ip" , "message" , "code" . Plus quotes around every key and string value.