diff --git a/lib/manifique/agent.rb b/lib/manifique/agent.rb
index 1b30556..042c781 100644
--- a/lib/manifique/agent.rb
+++ b/lib/manifique/agent.rb
@@ -1,15 +1,31 @@
+require 'uri'
 require "manifique/web_client"
 
 module Manifique
   class Agent
-    def initialize(options)
+    def initialize(options={})
       @options = options
-      @url = options[:url]
+
+      if url_valid?(options[:url])
+        @url = options[:url]
+      else
+        raise "No valid URL specified"
+      end
     end
 
     def fetch_metadata
       web_client = WebClient.new(url: @url)
       web_client.fetch_web_manifest
     end
+
+    private
+
+    def url_valid?(str)
+      return false unless str.class == String
+      url = URI.parse(str)
+      url.kind_of?(URI::HTTP) || url.kind_of?(URI::HTTPS)
+    rescue URI::InvalidURIError
+      false
+    end
   end
 end
diff --git a/test/manifique_test.rb b/test/manifique_test.rb
index 202a046..5377f6f 100644
--- a/test/manifique_test.rb
+++ b/test/manifique_test.rb
@@ -5,6 +5,14 @@ class ManifiqueTest < Minitest::Test
     refute_nil ::Manifique::VERSION
   end
 
+  def test_init_without_url
+    assert_raises(RuntimeError) { Manifique::Agent.new }
+  end
+
+  def test_init_with_invalid_url
+    assert_raises(RuntimeError) { Manifique::Agent.new(url: "htp:/foo.com") }
+  end
+
   def test_fetch_metadata
     agent = Manifique::Agent.new(url: 'https://example.com')
     assert_equal agent.fetch_metadata, 'https://example.com'