diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index edd526c..6151513 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -13,4 +13,4 @@ updates:
       time: "12:00"
       timezone: "Europe/Berlin"
     assignees:
-      - "simonneutert"
\ No newline at end of file
+      - "simonneutert"
diff --git a/.github/workflows/ruby.yml b/.github/workflows/ruby.yml
index 4466911..bb5e2bd 100644
--- a/.github/workflows/ruby.yml
+++ b/.github/workflows/ruby.yml
@@ -38,6 +38,6 @@ jobs:
           bundle config path vendor/bundle
           bundle install --jobs 4 --retry 3
       - name: Run tests
-        run: bundle exec rake
+        run: bundle exec rubocop && bundle exec rake
         env:
           RACK_ENV: test
diff --git a/.rubocop b/.rubocop
new file mode 100644
index 0000000..bec972c
--- /dev/null
+++ b/.rubocop
@@ -0,0 +1 @@
+--server
\ No newline at end of file
diff --git a/.rubocop.yml b/.rubocop.yml
new file mode 100644
index 0000000..ac39c31
--- /dev/null
+++ b/.rubocop.yml
@@ -0,0 +1,33 @@
+# The behavior of RuboCop can be controlled via the .rubocop.yml
+# configuration file. It makes it possible to enable/disable
+# certain cops (checks) and to alter their behavior if they accept
+# any parameters. The file can be placed either in your home
+# directory or in some project directory.
+#
+# RuboCop will start looking for the configuration file in the directory
+# where the inspected file is and continue its way up to the root directory.
+#
+# See https://docs.rubocop.org/rubocop/configuration
+
+
+AllCops:
+  TargetRubyVersion: 3.0
+  NewCops: enable
+
+Metrics/AbcSize:
+  Exclude:
+    - test/**/*
+
+Style/Documentation:
+  Enabled: false
+
+Metrics/ClassLength:
+  Exclude:
+    - app.rb
+
+Metrics/BlockLength:
+  Exclude:
+    - app.rb
+
+Metrics/MethodLength:
+  Max: 20
\ No newline at end of file
diff --git a/Gemfile b/Gemfile
index cfe179a..7d278d3 100644
--- a/Gemfile
+++ b/Gemfile
@@ -2,16 +2,14 @@
 
 source 'https://rubygems.org'
 
+gem 'puma', '~> 6.4'
 gem 'rack-unreloader', '~> 2.1'
 gem 'rackup', '~> 2.1.0'
 gem 'rake', '~> 13.0'
-gem 'roda', '~> 3.73'
-gem 'tilt', '~> 2.3'
-
 gem 'redcarpet', '~> 3.6'
+gem 'roda', '~> 3.73'
 gem 'tantiny', '0.3.3'
-
-gem 'puma', '~> 6.4'
+gem 'tilt', '~> 2.3'
 
 group :development do
   gem 'htmlbeautifier', require: false
diff --git a/Rakefile b/Rakefile
index 25ca87a..895cab2 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'minitest'
 require 'minitest/test_task'
 
diff --git a/app.rb b/app.rb
index 8a66233..f9c6f23 100644
--- a/app.rb
+++ b/app.rb
@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-
 # TODO: write a method for whitelist checks of media type
 MEDIA_WHITELIST = %w[txt pdf md png jpg jpeg heic webp yml yaml json]
                   .map { |c| [c.upcase, c] }
@@ -19,8 +18,10 @@ class App < Roda
   plugin :render, layout: './layout'
   plugin :view_options
   plugin :all_verbs
+  # rubocop:disable Layout/LineLength
   plugin :sessions, key: 'labradorite',
                     secret: ENV.delete('SESSION_SECRET') || 'labradoritelabradoritelabradoritelabradoritelabradoritelabradorite'
+  # rubocop:enable Layout/LineLength
   plugin :caching
   plugin :json
   plugin :json_parser
@@ -181,7 +182,7 @@ class App < Roda
         new_memo = FileOperations::NewMemoGenerator.new
         new_memo.generate
         r.redirect "/#{new_memo.path}/edit"
-      rescue StandardError => e
+      rescue StandardError
         r.redirect '/memos/new'
       end
 
diff --git a/lib/controllers/memos/search.rb b/lib/controllers/memos/search.rb
index dc21d59..3a26298 100644
--- a/lib/controllers/memos/search.rb
+++ b/lib/controllers/memos/search.rb
@@ -5,8 +5,8 @@ module Memos
     class Search
       attr_reader :r, :meta, :meta_ostruct, :index
 
-      def initialize(r, index)
-        @params = Helper::DeepCopy.create(r.params)
+      def initialize(req, index)
+        @params = Helper::DeepCopy.create(req.params)
         @index = index
         @search_input = @params['search']
       end
diff --git a/lib/controllers/memos/update.rb b/lib/controllers/memos/update.rb
index e532117..405ca3e 100644
--- a/lib/controllers/memos/update.rb
+++ b/lib/controllers/memos/update.rb
@@ -5,8 +5,8 @@ module Memos
     class Update
       attr_reader :r, :meta, :meta_ostruct, :index
 
-      def initialize(r, index, memo_path, meta)
-        @params = Helper::DeepCopy.create(r.params)
+      def initialize(req, index, memo_path, meta)
+        @params = Helper::DeepCopy.create(req.params)
         @index = index
         @memo_path = memo_path
         @meta = meta
diff --git a/lib/file_operations/attachments/deleter.rb b/lib/file_operations/attachments/deleter.rb
index 67298cb..cca0eae 100644
--- a/lib/file_operations/attachments/deleter.rb
+++ b/lib/file_operations/attachments/deleter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module FileOperations
   module Attachments
     class Deleter
diff --git a/lib/file_operations/delete_memo.rb b/lib/file_operations/delete_memo.rb
index ffd6b24..b9ff706 100644
--- a/lib/file_operations/delete_memo.rb
+++ b/lib/file_operations/delete_memo.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module FileOperations
   #
   # Deletes a Memo and its Meta Data and Attachments
diff --git a/lib/file_operations/files_sort_by_latest_modified.rb b/lib/file_operations/files_sort_by_latest_modified.rb
index 3c60697..45b14f6 100644
--- a/lib/file_operations/files_sort_by_latest_modified.rb
+++ b/lib/file_operations/files_sort_by_latest_modified.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module FileOperations
   #
   # Scans the filesystem and returns the latest modified file(paths)
@@ -10,9 +12,9 @@ class FilesSortByLatestModified
     #
     # @return [Array<String>] file paths from latest to touch to least touched
     #
-    def latest_n_memos_by_file_modified(n)
+    def latest_n_memos_by_file_modified(num)
       all_files_order_from_least_to_newest_modified
-        .last(n)
+        .last(num)
         .map! { |file_path| File.dirname(file_path) }
         .reverse
     end
diff --git a/lib/file_operations/memos/reload.rb b/lib/file_operations/memos/reload.rb
index 7f6ff73..4ea505d 100644
--- a/lib/file_operations/memos/reload.rb
+++ b/lib/file_operations/memos/reload.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Controllers
   module Memos
     class Reload
diff --git a/lib/file_operations/meta_data_file_reader.rb b/lib/file_operations/meta_data_file_reader.rb
index cc97598..92ab0ff 100644
--- a/lib/file_operations/meta_data_file_reader.rb
+++ b/lib/file_operations/meta_data_file_reader.rb
@@ -8,7 +8,7 @@ def from_path(path_string)
       end
 
       def hash_to_ostruct(meta_data)
-        OpenStruct.new(meta_data)
+        OpenStruct.new(meta_data) # rubocop:disable Style/OpenStructUse
       end
 
       #
diff --git a/lib/file_operations/new_memo_generator.rb b/lib/file_operations/new_memo_generator.rb
index b7065a6..c6e6245 100644
--- a/lib/file_operations/new_memo_generator.rb
+++ b/lib/file_operations/new_memo_generator.rb
@@ -1,8 +1,12 @@
+# frozen_string_literal: true
+
 module FileOperations
   class NewMemoGenerator
     attr_reader :slug, :path
 
-    def initialize; end
+    def initialize
+      # overwrite this, if needed
+    end
 
     def generate
       @slug = Helper::SimpleUidGenerator.generate
diff --git a/lib/helper/simple_uid_generator.rb b/lib/helper/simple_uid_generator.rb
index 813610d..8ff9069 100644
--- a/lib/helper/simple_uid_generator.rb
+++ b/lib/helper/simple_uid_generator.rb
@@ -6,7 +6,7 @@ class << self
       def generate
         8.times.map do
           ('a'..'z').to_a.sample
-        end.join('').insert(4, '-')
+        end.join.insert(4, '-')
       end
     end
   end
diff --git a/lib/search_index/core.rb b/lib/search_index/core.rb
index c98e6eb..de85b7b 100644
--- a/lib/search_index/core.rb
+++ b/lib/search_index/core.rb
@@ -55,7 +55,8 @@ def recreate_index!
     # TODO: extract paths to constants
     def extract_data_from_files
       Dir.glob(MARKDOWN_DIR).map do |file|
-        meta = YAML.safe_load_file(file.gsub(MARKDOWN_FILENAME, META_FILENAME), permitted_classes: [Date, Time, DateTime])
+        meta = YAML.safe_load_file(file.gsub(MARKDOWN_FILENAME, META_FILENAME),
+                                   permitted_classes: [Date, Time, DateTime])
         content = File.read(file)
         data = meta.merge({ 'content' => content })
         map_data_to_schema(data)
diff --git a/test/default_memos_test.rb b/test/default_memos_test.rb
index ad887aa..6ff40ec 100644
--- a/test/default_memos_test.rb
+++ b/test/default_memos_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require 'minitest/autorun'
-require_relative './test_helper'
+require_relative 'test_helper'
 
 class TestMemosOnFilesystem < Minitest::Test
   def test_memos_default
diff --git a/test/endpoints_api_v1_test.rb b/test/endpoints_api_v1_test.rb
index 5aa5709..6bd300c 100644
--- a/test/endpoints_api_v1_test.rb
+++ b/test/endpoints_api_v1_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require 'minitest/autorun'
-require_relative './test_helper'
+require_relative 'test_helper'
 
 class TestEndpointsApiV1 < Minitest::Test
   OUTER_APP = Rack::Builder.parse_file('config.ru')
@@ -26,6 +28,7 @@ def test_memos_tantiny_reload
     assert_equal json['status'], 'success'
   end
 
+  # rubocop:disable Layout/LineLength
   def test_memos_tantiny_search
     post '/api/v1/memos/reload'
 
@@ -45,6 +48,7 @@ def test_memos_tantiny_search
                   "![](/memos/2021/08/21/hgfe-dcba/665507228-pug.jpg)\r"], first_result_triplet.last
     assert_kind_of Array, first_result_triplet.last
   end
+  # rubocop:enable Layout/LineLength
 
   def test_memos_tantiny_search_without_match
     post '/api/v1/memos/reload'
@@ -71,6 +75,7 @@ def test_memos_markdown_to_html_preview
     assert_equal json['md'], "<h1>Labradorite</h1>\n"
   end
 
+  # rubocop:disable Layout/LineLength
   def test_memos_update_memo
     post('/api/v1/memos/2021/08/21/hgfe-dcba/update', { 'title' => 'Facts about Pugsies!',
                                                         'tags' => 'dog,pug,pet',
@@ -80,4 +85,5 @@ def test_memos_update_memo
     assert_equal last_response.status, 200
     assert_equal JSON.parse(last_response.body)['status'], 'success'
   end
+  # rubocop:enable Layout/LineLength
 end
diff --git a/test/endpoints_get_test.rb b/test/endpoints_get_test.rb
index 73fa1d9..21876e9 100644
--- a/test/endpoints_get_test.rb
+++ b/test/endpoints_get_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require 'minitest/autorun'
-require_relative './test_helper'
+require_relative 'test_helper'
 
 class TestEndpointsGet < Minitest::Test
   OUTER_APP = Rack::Builder.parse_file('config.ru')
diff --git a/test/meta_data_serializer_test.rb b/test/meta_data_serializer_test.rb
index 999b853..cbfb20a 100644
--- a/test/meta_data_serializer_test.rb
+++ b/test/meta_data_serializer_test.rb
@@ -1,9 +1,11 @@
+# frozen_string_literal: true
+
 require 'minitest/autorun'
 require_relative 'test_helper'
 
 class TestMetaDataSerializing < Minitest::Test
   def yaml_string
-    yaml_string = '''
+    '
 ---
 id: 2021/08/21/hgfe-dcba
 title: Facts about Pugs!
@@ -13,7 +15,7 @@ def yaml_string
 - http://localhost:9292/memos/2022/09/25/abcd-efgh/edit
 - http://localhost:9292/memos/2022/09/24/abcd-efgh/edit
 updated_at: !ruby/object:DateTime 2021-08-21 17:29:58.161601000 +02:00
-'''
+'
   end
 
   def setup
diff --git a/test/simple_uid_generator_test.rb b/test/simple_uid_generator_test.rb
index 04b401e..000a559 100644
--- a/test/simple_uid_generator_test.rb
+++ b/test/simple_uid_generator_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require 'minitest/autorun'
-require_relative './test_helper'
+require_relative 'test_helper'
 
 class TestSimpleUidGenerator < Minitest::Test
   def setup
diff --git a/test/test_helper.rb b/test/test_helper.rb
index e744246..88faa82 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 dev = ENV['RACK_ENV'] == 'development'
 
 require 'yaml'