RubyMCP - Build a MCP Server with Ruby

A low-level Model-Context-Protocol implementation for Ruby. Supports prompts and completions.

server = RubyMCP::Server.new

server.add_prompt(
  name: "ruby_example",
  description: "Example usage of a method",
  arguments: [
    {
      name: "snippet",
      description: "small ruby snippet",
      required: true,
      completions: ->(*) { [ 'String#split', 'Array#join', 'tally', 'unpack' ] }
    }
  ],
  result: ->(snippet:) {
    {
      description: "Explain '#{snippet}'",
      messages: [
        {
          role: "user",
          content: {
            type: "text",
            text: <<~TXT
              You're a coding assistant in the editor zed.
              You give one practical example for the given ruby method.
              Only answer with a single code snippet and one line of explanation.
              For example:
              INPUT: '''String#split'''
              OUTPUT: 'abc'.split('') # ['a', 'b', 'c']\n Splits the string"
            TXT
          }
        },
        {
          role: "user",
          content: {
            type: "text",
            text: "INPUT: '''#{snippet}'''"
          }
        }
      ]
    }
  },
)

transport = RubyMCP::Transport::Stdio.new
server.connect(transport)

Logging

RubyMCP supports mcp logging. Each logging level has a corresponding method prefixed with send_ and suffixed with _log_message.

• Debug Level:

  server.send_debug_log_message({ text: "Debug information" })

• Info Level:

  server.send_info_log_message({ text: "Informational message" })

A MCP client can configure change the log severity or it can be set during server creation. The default is "info".

server = Server.new(logging_verbosity: "debug")