MicroMcp

MicroMcp is a tiny framework for building MCP servers in Ruby. It ships with a Rust extension that handles the low level protocol while your Ruby code focuses on registering tools.

The gem is available on RubyGems.

Add the gem to your application's Gemfile:

gem "micro_mcp"

Then execute:

bundle install

Or install it directly with RubyGems:

gem install micro_mcp

Define one or more tools and start the server:

require "micro_mcp"

 MicroMcp::ToolRegistry.register_tool(name: "say_hello") do
  "Hello World!"
end

# Tools can also accept arguments defined using JSON Schema.
# The arguments hash is provided as the first block parameter.
 MicroMcp::ToolRegistry.register_tool(
  name: "add_numbers",
  description: "Adds two integers",
  arguments: {
    "type" => "object",
    "properties" => {
      "a" => {"type" => "integer"},
      "b" => {"type" => "integer"}
    },
    "required" => ["a", "b"]
  }
) do |args, _runtime|
  (args["a"] + args["b"]).to_s
end

MicroMcp.start_server

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/ekroon/micro_mcp.

The gem is available as open source under the terms of the MIT License.