diff --git a/Checks b/Checks
index c3a989f4..47847c57 100644
--- a/Checks
+++ b/Checks
@@ -1,7 +1,15 @@
-deploy_check :internal_links
-deploy_check :mixed_content
-deploy_check :stale
-deploy_check :no_unprocessed_erb
+require 'open3'
+require 'json'
+
+check :html5 do
+  cmd = "java -jar opt/validator/vnu.jar --format json --skip-non-html --schema http://s.validator.nu/html5-all.rnc #{@config[:output_dir]}"
+  res = Open3.popen3(cmd) { |_stdin, _stdout, stderr| stderr.read }
+
+  JSON.parse(res).fetch('messages', []).each do |err|
+    subject = err['url'].sub(/^file:#{Regexp.escape File.dirname(__FILE__)}\//, '')
+    add_issue("#{err['message']} (line #{err['lastLine']}, column #{err['firstColumn']})", subject: subject)
+  end
+end
 
 check :no_unprocessed_erb do
   @output_filenames.each do |filename|
@@ -11,4 +19,11 @@ check :no_unprocessed_erb do
   end
 end
 
+
+deploy_check :internal_links
+deploy_check :mixed_content
+deploy_check :stale
+deploy_check :no_unprocessed_erb
+deploy_check :no_unprocessed_markdown
+
 # vi: ft=ruby
diff --git a/opt/validator/VERSION b/opt/validator/VERSION
new file mode 100644
index 00000000..4f339b76
--- /dev/null
+++ b/opt/validator/VERSION
@@ -0,0 +1 @@
+16.10.27
\ No newline at end of file
diff --git a/opt/validator/vnu.jar b/opt/validator/vnu.jar
new file mode 100644
index 00000000..a53a4e08
Binary files /dev/null and b/opt/validator/vnu.jar differ