diff --git a/lib/tasks/dep.rake b/lib/tasks/dep.rake
new file mode 100644
index 0000000..d82c0c6
--- /dev/null
+++ b/lib/tasks/dep.rake
@@ -0,0 +1,59 @@
+namespace :dep do
+  desc "list dependency gems order by less referenced"
+  task :list do
+    require "set"
+    deps = Set.new
+    context = false
+    current_parent  = false
+    versions = {
+      "bundler" => "1.7.4" # bundler version does not appear in Gemfile.lock
+    }
+    skip_gems = %w(fluentd)
+    lock_file = "Gemfile.production.lock"
+    unless ENV["SKIP_BUNDLE_INSTALL"]
+      system("bundle install --gemfile Gemfile.production", out: STDERR) # ensure lock file is up to date
+    end
+
+    File.open(lock_file).each_line do |line|
+      # GEM
+      #   remote: https://rubygems.org/
+      #   specs:
+      #     foo_gem (0.1.2)
+      #       foo_dep1 (>= 1.0.0)
+      #       foo_dep2
+      #     bar_gem (1.2.1)
+      #       bar_dep1
+      #       ...
+      #   ...
+      if line == "  specs:\n"
+        context = true
+        next
+      end
+      gem_name = line[/[^ \n]+/, 0] # "    foo_gem (0.1.2)\n" => "foo_gem"
+      if line.match(/^ {4}[^ ]/)    # "    foo_gem (0.1.2)"
+        if skip_gems.include?(gem_name)
+          current_parent = nil
+          next
+        end
+        current_parent = gem_name
+        versions[current_parent] = line[/\((.*?)\)/, 1] # foobar (1.2.3) => 1.2.3
+        next
+      elsif line.match(/^ {6}[^ ]/) # "      foo_dep1 (>= 1.0.0)"
+        next if skip_gems.include?(gem_name)
+        next if current_parent.blank?
+        deps.add([current_parent, gem_name])
+      else
+        context = false
+      end
+    end
+    rank = {}
+    deps.to_a.each do |(parent, child)|
+      rank[parent] ||= 0
+      rank[child] ||= 0
+      rank[parent] += 1
+    end
+    rank.to_a.sort_by {|(name, score)| score }.each do |(name, score)|
+      puts %Q|download "#{name}", "#{versions[name]}"|
+    end
+  end
+end