MCP-RB

[!WARNING] This project is no longer maintained, and this repository will be archived.

Please use the official MCP Ruby SDK (mcp gem) instead. It is actively developed under the Model Context Protocol organization and supports the latest protocol features, including clients, prompts, and the Streamable HTTP transport.

gem "mcp"

Both mcp-rb and mcp are loaded with require "mcp" and define the top-level MCP module, so remove mcp-rb from your Gemfile when you switch. See the official documentation to get started.

A lightweight Ruby framework for implementing MCP (Model Context Protocol) servers with a Sinatra-like DSL.

Installation

Add this line to your application’s Gemfile:

gem 'mcp-rb'

Usage

Here’s a simple example of how to create an MCP server:

require 'mcp'

name "hello-world"

version "1.0.0"

# Define a resource
resource "hello://world" do
  name "Hello World"
  description "A simple hello world message"
  call { "Hello, World!" }
end

# Define a resource template
resource_template "hello://{user_name}" do
  name "Hello User"
  description "A simple hello user message"
  call { |args| "Hello, #{args[:user_name]}!" }
end

# Define a tool
tool "greet" do
  description "Greet someone by name"
  argument :name, String, required: true, description: "Name to greet"
  call do |args|
    "Hello, #{args[:name]}!"
  end
end

# Define a tool with nested arguments
tool "greet_full_name" do
  description "Greet someone by their full name"
  argument :person, required: true, description: "Person to greet" do
    argument :first_name, String, required: false, description: "First name"
    argument :last_name, String, required: false, description: "Last name"
  end
  call do |args|
    "Hello, First: #{args[:person][:first_name]} Last: #{args[:person][:last_name]}!"
  end
end

# Define a tool with an Array argument
tool "group_greeting" do
  description "Greet multiple people at once"
  argument :people, Array, required: true, items: String, description: "People to greet"
  call do |args|
    args[:people].map { |person| "Hello, #{person}!" }.join(", ")
  end
end

Supported specifications

Reference: MCP 2024-11-05

• Base Protocol
  • ping
  • stdio transport
• Server features
  • Resources
    • resources/read
    • resources/list
    • resources/templates/list
  • Tools
    • tools/list
    • tools/call

Any capabilities are not supported yet.

Testing

rake test
rake test:unit # run only the unit tests, skipping tests that test a running server

Test with MCP Inspector

bunx @modelcontextprotocol/inspector $(pwd)/examples/hello_world.rb

Formatting

bundle exec standardrb --fix

You can also use rake tasks:

rake lint      # Run standardrb to check code style
rake lint:fix  # Auto-fix standardrb issues

Release

To release a new version:

1. Update version in lib/mcp/version.rb
2. Update CHANGELOG.md
3. Create a git tag

git add .
git commit -m "Release vx.y.z"
git tag vx.y.z
git push --tags

1. Build and push to RubyGems

gem build mcp-rb.gemspec
gem push mcp-rb-*.gem

Changelog

See CHANGELOG.md