TOON MCP Server

MCP server exposing TOON format for LLM cost optimization. 18-40% token savings over JSON.

Repository: github.com/copyleftdev/toon-mcp

Demo

Installation

cargo build --release

Usage

Claude Desktop

Add to ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):

{
  "mcpServers": {
    "toon": {
      "command": "/path/to/toon-mcp"
    }
  }
}

Claude Code CLI

Add to ~/.claude/settings.json:

{
  "mcpServers": {
    "toon": {
      "command": "/path/to/toon-mcp"
    }
  }
}

Or for project-specific configuration, create .mcp.json in your project root:

{
  "mcpServers": {
    "toon": {
      "command": "/path/to/toon-mcp"
    }
  }
}

Cursor IDE

Add to .cursor/mcp.json in your project:

{
  "mcpServers": {
    "toon": {
      "command": "/path/to/toon-mcp"
    }
  }
}

Generic MCP Client

The server uses stdio transport. Connect by spawning the process and communicating via stdin/stdout:

# Start server and send initialize request
echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"my-client","version":"1.0"}}}' | ./toon-mcp

Example in Node.js:

const { spawn } = require('child_process');
const server = spawn('./toon-mcp');

server.stdout.on('data', (data) => {
  console.log('Response:', JSON.parse(data));
});

server.stdin.write(JSON.stringify({
  jsonrpc: "2.0",
  id: 1,
  method: "initialize",
  params: {
    protocolVersion: "2024-11-05",
    capabilities: {},
    clientInfo: { name: "my-client", version: "1.0" }
  }
}) + '\n');

Tools

toon_encode

Convert JSON to TOON format.

{"json": {"users": [{"id": 1, "name": "Alice"}]}}

Options:

• delimiter - "comma" (default), "tab", or "pipe"
• indent - Spaces for indentation (0-8, default: 2)
• fold_keys - Enable v1.5 key folding
• flatten_depth - Max depth for key folding

toon_decode

Convert TOON back to JSON.

{"toon": "name: Alice\nage: 30"}

Options:

• strict - Strict validation (default: true)
• coerce_types - Type coercion (default: true)
• expand_paths - Path expansion (default: false)
• output_format - "json" or "json_pretty" (default: "json")

toon_validate

Check TOON syntax without full decoding.

{"toon": "x: 1"}

Returns: {"valid": true} or {"valid": false, "error": {...}}

toon_stats

Compare token and byte counts between JSON and TOON.

{"json": {"data": [1, 2, 3]}}

Returns savings percentages for bytes and tokens.

toon_ping

Verify server connectivity.

Returns: "pong - toon-mcp server is running"

Development

cargo check          # Type check
cargo build          # Debug build
cargo build --release # Release build
cargo test           # Run all tests
cargo clippy         # Lint
cargo fmt            # Format

Contributing

Contributions are welcome! Please open an issue or submit a PR at github.com/copyleftdev/toon-mcp.

License

MIT - See LICENSE for details.