rubyhash-mcp

MCP server for RubyHash. Gives any MCP-capable agent (Claude Code, Claude Desktop, Cursor, and others) two deterministic Ruby tools:

• ruby_hash_diff: compare two Ruby hash literals, or paste raw failing Minitest/RSpec output, and get a structured report of exactly what changed: changed values with before and after, added and removed keys, and explicit type changes (nil to String, Integer to Float, symbol keys vs string keys).

• ruby_to_json: convert a Ruby hash or array literal (hashrockets, symbol keys, shorthand syntax, nesting, nil/true/false) to clean JSON with sorted keys.

Everything runs locally in the server process. Nothing is uploaded, logged, or stored, the same privacy promise as rubyhash.dev.

Tools

• ruby_hash_diff: Compare two Ruby hash literals, or paste raw failing Minitest/RSpec output, and get a structured report: changed values with before and after, added and removed keys, and explicit type changes (nil to String, Integer to Float, symbol keys vs string keys).

• ruby_to_json: Convert a Ruby hash or array literal (hashrockets, symbol keys, shorthand syntax, nesting, nil/true/false) to clean JSON with alphabetically sorted keys.

Related MCP server: JSON Compare MCP Server

Why an agent would want this

When a Ruby test fails on two large nearly identical hashes, comparing them by reading is slow and error prone, for humans and for language models. A 40-key nested hash diff burns context and invites mistakes. This server does the comparison with a real recursive descent parser and hands back only the differences, deterministically.

Install

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

Or for Claude Code:

claude mcp add rubyhash -- npx -y rubyhash-mcp

Example

Input (raw test output):

-{"uid"=>"u@example.test", "role"=>"admin", "seats"=>3}
+{"uid"=>"u@example.test", "role"=>"editor", "seats"=>3.0}

Output:

{
  "equal": false,
  "summary": "2 changed, 0 added, 0 removed, 1 type change",
  "changed": [
    { "path": "role", "before": "admin", "after": "editor", "typeChanged": false },
    { "path": "seats", "before": 3, "after": 3, "beforeType": "Integer", "afterType": "Float", "typeChanged": true }
  ]
}

Also available as an HTTP API

If you cannot run a local MCP server, the same tools are exposed at the RubyHash Agent API, with an OpenAPI description and an x402 machine-payable catalog.

Development

npm install
npm test   # 36 unit tests

License

MIT for this package. The rubyhash.dev site and its browser tool are separate, private, and all rights reserved.