diff --git a/.rubocop.yml b/.rubocop.yml
new file mode 100644
index 0000000..648dfb1
--- /dev/null
+++ b/.rubocop.yml
@@ -0,0 +1,6 @@
+AllCops:
+  Exclude:
+    - _site/**/*
+
+Metrics/LineLength:
+  Enabled: false
diff --git a/jekyll-theme-hacker.gemspec b/jekyll-theme-hacker.gemspec
index 5a9729b..6c7dc52 100644
--- a/jekyll-theme-hacker.gemspec
+++ b/jekyll-theme-hacker.gemspec
@@ -16,4 +16,8 @@ Gem::Specification.new do |s|
   s.platform      = Gem::Platform::RUBY
   s.add_runtime_dependency "jekyll", "~> 3.5"
   s.add_runtime_dependency "jekyll-seo-tag", "~> 2.0"
+  s.add_development_dependency 'w3c_validators', "~> 1.3"
+  s.add_development_dependency 'html-proofer', "~> 3.0"
+  s.add_development_dependency 'rubocop', "~> 0.50"
+
 end
diff --git a/script/cibuild b/script/cibuild
index 5a4da9a..b9a2962 100755
--- a/script/cibuild
+++ b/script/cibuild
@@ -3,4 +3,7 @@
 set -e
 
 bundle exec jekyll build
+bundle exec htmlproofer ./_site --check-html --disable-external
+bundle exec rubocop -D
+bundle exec script/validate-html
 gem build jekyll-theme-hacker.gemspec
diff --git a/script/validate-html b/script/validate-html
new file mode 100755
index 0000000..f6b17eb
--- /dev/null
+++ b/script/validate-html
@@ -0,0 +1,27 @@
+#!/usr/bin/env ruby
+
+require 'w3c_validators'
+
+def validator(file)
+  extension = File.extname(file)
+  if extension == '.html'
+    W3CValidators::NuValidator.new
+  elsif extension == '.css'
+    W3CValidators::CSSValidator.new
+  end
+end
+
+def validate(file)
+  puts "Checking #{file}..."
+
+  path = File.expand_path "../_site/#{file}", __dir__
+  results = validator(file).validate_file(path)
+
+  return puts 'Valid!' if results.errors.empty?
+
+  results.errors.each { |err| puts err.to_s }
+  exit 1
+end
+
+validate 'index.html'
+validate File.join 'assets', 'css', 'style.css'