diff --git a/ruby/Gemfile b/ruby/Gemfile
new file mode 100644
index 0000000..88bd7be
--- /dev/null
+++ b/ruby/Gemfile
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
+
+gem "minitest"
+gem "pry"
diff --git a/ruby/Gemfile.lock b/ruby/Gemfile.lock
new file mode 100644
index 0000000..911cc11
--- /dev/null
+++ b/ruby/Gemfile.lock
@@ -0,0 +1,19 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    coderay (1.1.3)
+    method_source (1.0.0)
+    minitest (5.16.2)
+    pry (0.14.1)
+      coderay (~> 1.1)
+      method_source (~> 1.0)
+
+PLATFORMS
+  arm64-darwin-21
+
+DEPENDENCIES
+  minitest
+  pry
+
+BUNDLED WITH
+   2.3.18
diff --git a/ruby/Rakefile b/ruby/Rakefile
new file mode 100644
index 0000000..bfd5f99
--- /dev/null
+++ b/ruby/Rakefile
@@ -0,0 +1,6 @@
+require "minitest/test_task"
+
+Minitest::TestTask.create do |t|
+  t.test_globs = "./test_*.rb"
+end
+task default: :test
diff --git a/ruby/lox.rb b/ruby/lox.rb
new file mode 100755
index 0000000..af9d26d
--- /dev/null
+++ b/ruby/lox.rb
@@ -0,0 +1,51 @@
+#!/usr/bin/env ruby -w
+
+module Lox
+  class << self
+    @had_error = false
+  end
+
+  def self.run_prompt
+    loop do
+      print "> "
+      line = gets
+      break if line.empty?
+      run(line)
+      @had_error = false
+    end
+  end
+
+  def self.run_file(io)
+    run(io.read)
+
+    exit 65 if @had_error
+  end
+
+  def self.run(src)
+    scanner = Scanner.new(src)
+    tokens = scanner.scan()
+
+    tokens.each do |token|
+      puts token
+    end
+  end
+
+  def self.error(line, msg)
+    report(line, "", msg)
+  end
+
+  def self.report(line, where, message)
+    puts "[line #{line}] Error#{where}: #{message}"
+    @had_error = true;
+  end
+end
+
+if __FILE__ == $0
+  puts "Usage: #$0 [script]" or exit 64 if ARGV.length > 1
+
+  if ARGV.empty?
+    Lox.run_prompt
+  else
+    Lox.run_file(ARGF)
+  end
+end
diff --git a/ruby/test_lox.rb b/ruby/test_lox.rb
new file mode 100644
index 0000000..1424231
--- /dev/null
+++ b/ruby/test_lox.rb
@@ -0,0 +1,14 @@
+require "minitest/autorun"
+
+require "lox"
+
+require "open3"
+require "pry"
+
+class TestLox < Minitest::Test
+  def test_error_on_more_than_one_arg
+    o, s = Open3.capture2("./lox.rb foo bar")
+    assert_equal 64, s.exitstatus
+    assert_equal "Usage: ./lox.rb [script]\n", o
+  end
+end