diff --git a/.github/scripts/test-gem.sh b/.github/scripts/test-gem.sh
index 75284644..36d30ec5 100755
--- a/.github/scripts/test-gem.sh
+++ b/.github/scripts/test-gem.sh
@@ -167,6 +167,7 @@ test_gem() {
 
     file="${workdir}/_site/index.html"
 
+    file_contains "${file}" "This is a fixture"
     file_contains "${file}" "class=\"${class}\""
     file_contains "${file}" "<svg"
     file_contains "${file}" "<ellipse"
diff --git a/lib/kramdown-plantuml/jekyll_page_processor.rb b/lib/kramdown-plantuml/jekyll_page_processor.rb
new file mode 100644
index 00000000..3d288d7a
--- /dev/null
+++ b/lib/kramdown-plantuml/jekyll_page_processor.rb
@@ -0,0 +1,105 @@
+# frozen_string_literal: true
+
+require 'htmlentities'
+require 'json'
+require_relative 'log_wrapper'
+
+module Kramdown
+  module PlantUml
+    # Processes Jekyll pages.
+    class JekyllPageProcessor
+      PROCESSED_KEY = :kramdown_plantuml_processed
+
+      def initialize(page)
+        raise ArgumentError, 'page cannot be nil' if page.nil?
+
+        puts page.class
+
+        @page = page
+      end
+
+      def process(site_destination_directory)
+        @page.output = do_process
+        @page.data[PROCESSED_KEY] = true
+        @page.write(site_destination_directory)
+      end
+
+      def should_process?
+        return false unless @page.output_ext == '.html'
+
+        if !@page.data.nil? && @page.data.key?(PROCESSED_KEY) && @page.data[PROCESSED_KEY]
+          logger.debug "Skipping #{@page.path} because it has already been processed."
+          return false
+        end
+
+        true
+      end
+
+      class << self
+        def needle(plantuml, options)
+          hash = { 'plantuml' => plantuml, 'options' => options.to_h }
+
+          <<~NEEDLE
+            <!--#kramdown-plantuml.start#-->
+            #{hash.to_json}
+            <!--#kramdown-plantuml.end#-->
+          NEEDLE
+        rescue StandardError => e
+          raise e if options.nil? || options.raise_errors?
+
+          logger.error 'Error while placing needle.'
+          logger.error e.to_s
+          logger.debug_multiline plantuml
+        end
+
+        def logger
+          @logger ||= ::Kramdown::PlantUml::LogWrapper.init
+        end
+      end
+
+      private
+
+      def do_process
+        logger.debug "Replacing Jekyll needles in #{@page.path}"
+
+        html = @page.output
+
+        return html if html.nil? || html.empty? || !html.is_a?(String)
+
+        html.gsub(/<!--#kramdown-plantuml\.start#-->(?<json>.*?)<!--#kramdown-plantuml\.end#-->/m) do
+          json = $LAST_MATCH_INFO ? $LAST_MATCH_INFO[:json] : nil
+          replace_needle(json) unless json.nil?
+        end
+      end
+
+      def replace_needle(json)
+        logger.debug 'Replacing Jekyll needle.'
+
+        needle_hash = JSON.parse(json)
+        options_hash = needle_hash['options']
+        options = ::Kramdown::PlantUml::Options.new({ plantuml: options_hash })
+
+        begin
+          decode_and_convert(needle_hash, options)
+        rescue StandardError => e
+          raise e if options.raise_errors?
+
+          logger.error 'Error while replacing Jekyll needle.'
+          logger.error e.to_s
+          logger.debug_multiline json
+        end
+      end
+
+      def decode_and_convert(hash, options)
+        encoded_plantuml = hash['plantuml']
+        plantuml = HTMLEntities.new.decode encoded_plantuml
+        diagram = ::Kramdown::PlantUml::Diagram.new(plantuml, options)
+        diagram.convert_to_svg
+      end
+
+      def logger
+        @logger ||= ::Kramdown::PlantUml::LogWrapper.init
+      end
+    end
+  end
+end
diff --git a/lib/kramdown-plantuml/jekyll_provider.rb b/lib/kramdown-plantuml/jekyll_provider.rb
index ab345a23..04914459 100644
--- a/lib/kramdown-plantuml/jekyll_provider.rb
+++ b/lib/kramdown-plantuml/jekyll_provider.rb
@@ -1,10 +1,7 @@
 # frozen_string_literal: true
 
-require 'json'
-require 'English'
-require 'htmlentities'
 require_relative 'log_wrapper'
-require_relative 'diagram'
+require_relative 'jekyll_page_processor'
 
 module Kramdown
   module PlantUml
@@ -32,20 +29,7 @@ def installed?
         end
 
         def needle(plantuml, options)
-          hash = { 'plantuml' => plantuml, 'options' => options.to_h }
-
-          <<~NEEDLE
-            <!--#kramdown-plantuml.start#-->
-            #{hash.to_json}
-            <!--#kramdown-plantuml.end#-->
-          NEEDLE
-        rescue StandardError => e
-          raise e if options.raise_errors?
-
-          puts e
-          logger.error 'Error while placing needle.'
-          logger.error e.to_s
-          logger.debug_multiline plantuml
+          JekyllPageProcessor.needle(plantuml, options)
         end
 
         private
@@ -63,54 +47,23 @@ def find_site_destination_dir
 
         def register_hook
           Jekyll::Hooks.register :site, :post_write do |site|
-            logger.debug ':site:post_write triggered.'
-
-            @site_destination_dir ||= site.dest
-
-            site.pages.each do |page|
-              page.output = replace_needles(page)
-              page.write(@site_destination_dir)
-            end
+            site_post_write(site)
           end
         end
 
-        def replace_needles(page)
-          logger.debug "Replacing Jekyll needle in #{page.path}"
-
-          html = page.output
-          return html if html.nil? || html.empty? || !html.is_a?(String)
+        def site_post_write(site)
+          logger.debug 'Jekyll:site:post_write triggered.'
+          @site_destination_dir ||= site.dest
 
-          html.gsub(/<!--#kramdown-plantuml\.start#-->(?<json>.*?)<!--#kramdown-plantuml\.end#-->/m) do
-            json = $LAST_MATCH_INFO[:json]
-            return replace_needle(json)
-          end
-        end
+          site.pages.each do |page|
+            processor = JekyllPageProcessor.new(page)
 
-        def replace_needle(json)
-          logger.debug 'Replacing Jekyll needle.'
+            next unless processor.should_process?
 
-          needle_hash = JSON.parse(json)
-          options_hash = needle_hash['options']
-          options = ::Kramdown::PlantUml::Options.new({ plantuml: options_hash })
-
-          begin
-            decode_and_convert(needle_hash, options)
-          rescue StandardError => e
-            raise e if options.raise_errors?
-
-            logger.error 'Error while replacing Jekyll needle.'
-            logger.error e.to_s
-            logger.debug_multiline json
+            processor.process(site.dest)
           end
         end
 
-        def decode_and_convert(hash, options)
-          encoded_plantuml = hash['plantuml']
-          plantuml = HTMLEntities.new.decode encoded_plantuml
-          diagram = ::Kramdown::PlantUml::Diagram.new(plantuml, options)
-          diagram.convert_to_svg
-        end
-
         def load_jekyll
           require 'jekyll'
           ::Jekyll
diff --git a/spec/jekyll_page_processor_spec.rb b/spec/jekyll_page_processor_spec.rb
new file mode 100644
index 00000000..a4746179
--- /dev/null
+++ b/spec/jekyll_page_processor_spec.rb
@@ -0,0 +1,99 @@
+# frozen_string_literal: true
+
+require 'rspec/its'
+require 'kramdown-plantuml/options'
+require 'kramdown-plantuml/jekyll_page_processor'
+
+Options = Kramdown::PlantUml::Options
+JekyllPageProcessor = ::Kramdown::PlantUml::JekyllPageProcessor
+
+describe JekyllPageProcessor do
+  let(:page) do
+    page = double('page')
+    allow(page).to receive(:output).and_return(output)
+    allow(page).to receive(:output=)
+    allow(page).to receive(:output_ext).and_return(output_ext)
+    allow(page).to receive(:data).and_return({})
+    allow(page).to receive(:write)
+    allow(page).to receive(:path).and_return(File.join(__dir__, 'page.md'))
+    page
+  end
+
+  subject { JekyllPageProcessor.new(page) }
+
+  describe '#initialize' do
+    context 'when page is nil' do
+      let(:page) { nil }
+      it { expect { subject }.to raise_error(ArgumentError, 'page cannot be nil') }
+    end
+  end
+
+  describe '#needle' do
+    subject { JekyllPageProcessor.needle(plantuml, options) }
+
+    context 'with nil :options' do
+      let(:options) { nil }
+      let(:plantuml) { "@startuml\n@enduml" }
+
+      it do
+        is_expected.to eq <<~NEEDLE
+          <!--#kramdown-plantuml.start#-->
+          {"plantuml":"@startuml\\n@enduml","options":{}}
+          <!--#kramdown-plantuml.end#-->
+        NEEDLE
+      end
+    end
+
+    context 'with nil :plantuml' do
+      let(:options) { Options.new }
+      let(:plantuml) { nil }
+
+      it do
+        is_expected.to eq <<~NEEDLE
+          <!--#kramdown-plantuml.start#-->
+          {"plantuml":null,"options":{}}
+          <!--#kramdown-plantuml.end#-->
+        NEEDLE
+      end
+    end
+
+    context 'with valid :options and :plantuml' do
+      let(:options) { { theme: { name: 'custom' } } }
+      let(:plantuml) { "@startuml\n@enduml" }
+
+      it do
+        is_expected.to eq <<~NEEDLE
+          <!--#kramdown-plantuml.start#-->
+          {"plantuml":"@startuml\\n@enduml","options":{"theme":{"name":"custom"}}}
+          <!--#kramdown-plantuml.end#-->
+        NEEDLE
+      end
+    end
+  end
+
+  describe '#process' do
+    before { subject.process(__dir__) }
+
+    context 'with HTML output' do
+      let(:output) { '<h1 id="hello">Hello</h1>' }
+      let(:output_ext) { '.html' }
+      its(:should_process?) { is_expected.to eq false }
+      it { expect(page.output).to eq output }
+    end
+  end
+
+  describe '#should_process?' do
+    context 'with HTML output' do
+      let(:output) { '<h1 id="hello">Hello</h1>' }
+      let(:output_ext) { '.html' }
+      its(:should_process?) { is_expected.to eq true }
+      it { expect(page.output).to eq output }
+    end
+
+    context 'with CSS output' do
+      let(:output) { 'body { display: none }' }
+      let(:output_ext) { '.css' }
+      its(:should_process?) { is_expected.to eq false }
+    end
+  end
+end
diff --git a/spec/jekyll_provider_spec.rb b/spec/jekyll_provider_spec.rb
index 60b81b38..e1739875 100644
--- a/spec/jekyll_provider_spec.rb
+++ b/spec/jekyll_provider_spec.rb
@@ -51,7 +51,7 @@
           'config' => File.join(jekyll_source, '_config.yml'),
           'incremental' => false,
           'source' => jekyll_source,
-          'verbose' => false,
+          'verbose' => ENV.fetch('DEBUG', false),
           'destination' => jekyll_destination
         })
       end
@@ -60,6 +60,7 @@
 
       context 'when plantuml contains HTML entities', :jekyll do
         it { is_expected.to match(/<div class="plantuml"><svg.*<\/svg><\/div>/m) }
+        it { is_expected.to match(/<h1.*>This is a fixture<\/h1>/m) }
       end
     end
   end