TOON MCP Server

A Model Context Protocol (MCP) server that provides tools for encoding and decoding TOON (Token-Oriented Object Notation).

TOON is a compact, human-readable format designed to represent JSON data using significantly fewer tokens, making it ideal for LLM prompts and context optimization.

👉 Learn more about the format at toonformat.dev

Features

This server exposes two core tools to MCP clients (specifically tested with Gemini CLI):

• encode_toon: Converts JSON strings into TOON format to save tokens.
• decode_toon: Converts TOON formatted text back into standard JSON.

Usage

Quick Start with Gemini CLI

To use this server with the Gemini CLI, follow these steps:

1. Install Gemini CLI (if you haven't already):

   npm install -g @google/gemini-cli@latest
   

2. Configure the MCP Server: You can register the server by creating or editing your Gemini settings file, typically located at ~/.gemini/settings.json (Global) or .gemini/settings.json (Project-local).

   Add the following configuration:

   {
     "mcpServers": {
       "toon": {
         "command": "npx",
         "args": ["-y", "git+https://github.com/kweinmeister/toon-mcp.git"]
       }
     }
   }
   

3. Run Gemini CLI: Start the CLI interface. The tools should now be available to the model.

   gemini
   

Tools

1. encode_toon

Converts JSON data into the compact TOON format.

Parameters:

Parameter	Type	Default	Description
json	string	Required	The JSON data (serialized as a string) to encode.
indent	number	2	Number of spaces for indentation.
delimiter	string	,	Delimiter for arrays/rows. Options: , (comma), \t (tab), | (pipe).
keyFolding	string	"off"	Collapse single-key wrapper chains (e.g., a.b.c). Options: "off", "safe".
flattenDepth	number	Infinity	Maximum depth to apply key folding.
replacer	(string|number)[]	undefined	Array of properties to include in the output.

Example Prompt in Gemini CLI:

"Use the encode_toon tool to convert this JSON into TOON format: {"users": [{"id": 1, "name": "Alice"}, {"id": 2, "name": "Bob"}]}"

Output:

users[2]{id,name}:
  1,Alice
  2,Bob

2. decode_toon

Parses TOON formatted text back into standard JSON.

Parameters:

Parameter	Type	Default	Description
toon	string	Required	The TOON formatted string to decode.
strict	boolean	true	Enforce strict validation (e.g., checking declared array lengths).
expandPaths	string	"off"	Reconstruct dotted keys into nested objects. Options: "off", "safe".
indent	number	2	Number of spaces for indentation.

Transports

This server supports both HTTP Server-Sent Events (SSE) and Standard IO (stdio).

HTTP / SSE (Default)

Useful for remote deployments (like Cloud Run) or web-based MCP clients.

# Starts on port 8080 by default
npm start

# Custom port
npm start -- --port 3000

Stdio

Used by local clients like Gemini CLI.

npm run start:stdio

Development

Installation

git clone https://github.com/kweinmeister/toon-mcp
cd toon-mcp
npm install

Testing

Run the unit tests to ensure the server tools are functioning correctly:

npm test

Debugging with MCP Inspector

You can use the MCP Inspector to inspect and test the server's tools interactively via a web interface.

npx fastmcp inspect index.ts

Building & Linting

# Linting
npx biome check .

# Type checking
npx tsc --noEmit