TOON format support for Java via json-io (40-50% token savings)

[jdereg]

Following up on issue #4869 requesting TOON support - wanted to share that there's now a Java library with full TOON read/write support that works with Spring AI today.

What is TOON?

TOON (Token-Oriented Object Notation) is a format designed for LLM efficiency, achieving ~40-50% token reduction vs JSON.

JSON (48 chars, ~15 tokens):

{"name":"John","age":30,"tags":["java","json"]}                                                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                                                                                                       
TOON (38 chars, ~9 tokens):                                                                                                                                                                                                                                                                                            
name: John                                                                                                                                                                                                                                                                                                             
age: 30                                                                                                                                                                                                                                                                                                                
tags[2]: java,json                                                                                                                                                                                                                                                                                                     

Using with Spring AI

  // Custom ToolCallResultConverter using TOON                                                                                                                                                                                                                                                                           
  String toon = JsonIo.toToon(toolResult, writeOptions);                                                                                                                                                                                                                                                                 
                                                                                                                                                                                                                                                                                                                         
  // Parsing TOON responses                                                                                                                                                                                                                                                                                              
  MyResponse response = JsonIo.fromToon(toonString, readOptions)                                                                                                                                                                                                                                                         
      .asClass(MyResponse.class);                                                                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                                                                                                         
  // With generics                                                                                                                                                                                                                                                                                                       
  List<Person> people = JsonIo.fromToon(toonString, readOptions)                                                                                                                                                                                                                                                         
      .asType(new TypeHolder<List<Person>>(){});                                                                                                                                                                                                                                                                         

Features

• Full TOON v1 spec read/write
• 55+ built-in types (all Java temporal types, UUID, URI, collections, etc.)
• Complex object graphs and generics support
• Maven: com.cedarsoftware:json-io:4.85.0

Links: https://github.com/jdereg/json-io | https://toonformat.dev/ | Related: #4869

Disclosure: I maintain json-io. Happy to answer questions or discuss integration patterns!