diff --git a/app/helpers/domain_helper.rb b/app/helpers/domain_helper.rb
new file mode 100644
index 0000000..f291fbc
--- /dev/null
+++ b/app/helpers/domain_helper.rb
@@ -0,0 +1,12 @@
+module DomainHelper
+  def normalize_domain(str)
+    str.strip.downcase
+  end
+
+  def tld(str)
+    parts = normalize_domain(str).split(".")
+    fail ArgumentError unless parts.size >= 2
+
+    ".#{parts.last}"
+  end
+end
diff --git a/test/helpers/domain_helper_test.rb b/test/helpers/domain_helper_test.rb
new file mode 100644
index 0000000..9b6cd59
--- /dev/null
+++ b/test/helpers/domain_helper_test.rb
@@ -0,0 +1,22 @@
+require "test_helper"
+require "domain_helper"
+
+class DomainHelperTest < ActiveSupport::TestCase
+  include DomainHelper
+
+  test "should normalize a domain name" do
+    assert_equal "example.org", normalize_domain(" example.org ")
+    assert_equal "example.org", normalize_domain("eXaMple.oRg")
+  end
+
+  test "tld should return the domain tld" do
+    assert_equal ".org", tld("exaMple.ORG")
+    assert_equal ".fr", tld("www.example.fr")
+    assert_equal ".com", tld("www.example-dashed.com")
+    assert_equal ".uk", tld("www.example.co.uk")
+
+    assert_raises(ArgumentError) do
+      tld("not a domain")
+    end
+  end
+end