jsonata-mcp

A Model Context Protocol (MCP) server that provides tools to evaluate and validate JSONata expressions. JSONata is a lightweight query and transformation language for JSON data.

Features

• Evaluate JSONata expressions against JSON data with a 5-second timeout for safety
• Validate JSONata syntax without execution
• Access JSONata function reference documentation for built-in functions

Installation

No manual install needed — use npx to run directly:

npx jsonata-mcp

Or install globally:

npm install -g jsonata-mcp
jsonata-mcp

The server communicates over stdio, so it's designed to be launched by an MCP client rather than run directly.

Usage

Claude Desktop

Add to your Claude Desktop config (claude_desktop_config.json):

{
  "mcpServers": {
    "jsonata": {
      "command": "npx",
      "args": ["jsonata-mcp"]
    }
  }
}

Claude Code

claude mcp add jsonata -- npx jsonata-mcp

Tools

evaluate_jsonata

Evaluate a JSONata expression against optional JSON data.

Parameters:

• expression (string, required) — the JSONata expression to evaluate
• data (any, optional) — JSON data to evaluate against

Example request:

{
  "name": "evaluate_jsonata",
  "arguments": {
    "expression": "items[price > 10].name",
    "data": {
      "items": [
        {"name": "Apple", "price": 5},
        {"name": "Laptop", "price": 1200},
        {"name": "Book", "price": 15}
      ]
    }
  }
}

Example response:

{
  "content": [
    {
      "type": "text",
      "text": "{\"success\":true,\"result\":[\"Laptop\",\"Book\"],\"expression\":\"items[price > 10].name\",\"data\":{\"items\":[{\"name\":\"Apple\",\"price\":5},{\"name\":\"Laptop\",\"price\":1200},{\"name\":\"Book\",\"price\":15}]}}"
    }
  ]
}

validate_jsonata

Validate if a string is valid JSONata syntax without evaluating it.

Parameters:

• expression (string, required) — the JSONata expression to validate

Example request:

{
  "name": "validate_jsonata",
  "arguments": {
    "expression": "users[age >= 18].{\"name\": name, \"adult\": true}"
  }
}

Example response:

{
  "content": [
    {
      "type": "text",
      "text": "{\"valid\":true,\"expression\":\"users[age >= 18].{\\\"name\\\": name, \\\"adult\\\": true}\",\"message\":\"Expression is valid JSONata syntax\"}"
    }
  ]
}

jsonata_function_reference

Get reference information about JSONata built-in functions.

Parameters:

• functionName (string, optional) — specific function to look up (e.g. $sum, $map)

Example request:

{
  "name": "jsonata_function_reference",
  "arguments": {
    "functionName": "$sum"
  }
}

Example response:

{
  "content": [
    {
      "type": "text",
      "text": "{\"function\":\"$sum\",\"description\":\"Returns the sum of an array of numbers\",\"category\":\"numeric\"}"
    }
  ]
}

Resources

• JSONata Documentation
• JSONata Exerciser — interactive playground
• JSONata GitHub

Development

npm run dev     # watch mode (recompiles on change)
npm test        # run tests
npm run build   # compile TypeScript