diff --git a/app/controllers/analytics_controller.rb b/app/controllers/analytics_controller.rb
index de765ceb0b..472120a92a 100644
--- a/app/controllers/analytics_controller.rb
+++ b/app/controllers/analytics_controller.rb
@@ -121,7 +121,7 @@ def campaign_stats
 
   def campaign_intersection
     set_campaigns
-    campaign_name = @campaign_1.title + ' + ' + @campaign_2.title
+    campaign_name = "#{@campaign_1.title} + #{@campaign_2.title}"
     campaign_1_course_ids = @campaign_1.courses.pluck(:id)
     course_ids = @campaign_2.courses.where(id: campaign_1_course_ids).pluck(:id)
 
diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index bb5aa913a6..0b034a6c74 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -35,7 +35,7 @@ def hot_javascript_path(filename)
   def fingerprinted(path, filename, file_prefix = nil)
     manifest_path = "#{Rails.root}/public/#{path}/manifest.json"
     manifest = Oj.load(File.read(File.expand_path(manifest_path, __FILE__)))
-    "#{file_prefix}#{manifest[filename + '.js']}"
+    "#{file_prefix}#{manifest["#{filename}.js"]}"
   end
 
   def css_fingerprinted(filename)
diff --git a/app/helpers/surveys_helper.rb b/app/helpers/surveys_helper.rb
index f2d4c762e4..f13efb9915 100644
--- a/app/helpers/surveys_helper.rb
+++ b/app/helpers/surveys_helper.rb
@@ -28,7 +28,7 @@ def survey_preview_url(survey)
   def question_answer_field_name(form, multiple)
     name = "answer_group[#{form.object.question_id}][answer_text]"
     if multiple
-      name + '[]'
+      "#{name}[]"
     else
       name
     end
diff --git a/app/mailers/fall2017_cmu_experiment_mailer.rb b/app/mailers/fall2017_cmu_experiment_mailer.rb
index 103fab4fe7..239488d80f 100644
--- a/app/mailers/fall2017_cmu_experiment_mailer.rb
+++ b/app/mailers/fall2017_cmu_experiment_mailer.rb
@@ -11,7 +11,7 @@ def email(course, instructor, email_code, reminder: false)
     @course = course
     @instructor = instructor
     subject = 'Peer support for students in your Wikipedia assignment'
-    subject = 'Reminder: ' + subject if reminder
+    subject = "Reminder: #{subject}" if reminder
     @opt_in_link = "https://#{ENV['dashboard_url']}/experiments/fall2017_cmu_experiment/"\
                    "#{@course.id}/#{email_code}/opt_in"
     @opt_out_link = "https://#{ENV['dashboard_url']}/experiments/fall2017_cmu_experiment/"\
diff --git a/app/mailers/spring2018_cmu_experiment_mailer.rb b/app/mailers/spring2018_cmu_experiment_mailer.rb
index 6bff80293c..7f6f17bd17 100644
--- a/app/mailers/spring2018_cmu_experiment_mailer.rb
+++ b/app/mailers/spring2018_cmu_experiment_mailer.rb
@@ -11,7 +11,7 @@ def email(course, instructor, email_code, reminder: false)
     @course = course
     @instructor = instructor
     subject = 'Peer support for students in your Wikipedia assignment'
-    subject = 'Reminder: ' + subject if reminder
+    subject = "Reminder: #{subject}" if reminder
     @opt_in_link = "https://#{ENV['dashboard_url']}/experiments/spring2018_cmu_experiment/"\
                    "#{@course.id}/#{email_code}/opt_in"
     @opt_out_link = "https://#{ENV['dashboard_url']}/experiments/spring2018_cmu_experiment/"\
diff --git a/app/mailers/suspected_plagiarism_mailer.rb b/app/mailers/suspected_plagiarism_mailer.rb
index da553d29ac..f56665eccf 100644
--- a/app/mailers/suspected_plagiarism_mailer.rb
+++ b/app/mailers/suspected_plagiarism_mailer.rb
@@ -17,7 +17,7 @@ def content_expert_email(alert, content_experts)
     @article_url = @article&.url
     @courses_user = @user.courses_users.last
     @course = alert.course
-    @talk_page_new_section_url = @courses_user.talk_page_url + '?action=edit&section=new'
+    @talk_page_new_section_url = "#{@courses_user.talk_page_url}?action=edit&section=new"
     @report_url = alert.url
     mail(to: @course.instructors.pluck(:email),
          cc: content_experts.pluck(:email),
diff --git a/app/mailers/ticket_notification_mailer.rb b/app/mailers/ticket_notification_mailer.rb
index ada0aa3a68..511c8347a2 100644
--- a/app/mailers/ticket_notification_mailer.rb
+++ b/app/mailers/ticket_notification_mailer.rb
@@ -60,6 +60,6 @@ def carbon_copy
 
   def email_subject
     subject_prefix = @course ? "#{@course.title}: " : ''
-    subject_prefix + 'Response to your help request'
+    "#{subject_prefix}Response to your help request"
   end
 end
diff --git a/app/models/wiki.rb b/app/models/wiki.rb
index 10e5e5e267..b2a8f9eb18 100644
--- a/app/models/wiki.rb
+++ b/app/models/wiki.rb
@@ -118,7 +118,7 @@ def domain
   end
 
   def base_url
-    'https://' + domain
+    "https://#{domain}"
   end
 
   def api_url
diff --git a/app/services/add_sandbox_template.rb b/app/services/add_sandbox_template.rb
index e1f181e37b..bc1e399009 100644
--- a/app/services/add_sandbox_template.rb
+++ b/app/services/add_sandbox_template.rb
@@ -44,7 +44,7 @@ def replace_default_with_sandbox_template
 
   def add_sandbox_template
     sandbox_summary = "adding #{@sandbox_template}"
-    new_line_template = @sandbox_template + "\n"
+    new_line_template = "#{@sandbox_template}\n"
     @wiki_editor.add_to_page_top(@sandbox, @current_user, new_line_template, sandbox_summary)
   end
 end
diff --git a/app/services/copy_course.rb b/app/services/copy_course.rb
index 003a7865db..0d076b02db 100644
--- a/app/services/copy_course.rb
+++ b/app/services/copy_course.rb
@@ -134,7 +134,7 @@ def retrieve_users_data
   end
 
   def retrieve_all_training_modules
-    dashboard_uri = URI.parse(@host + '/training_modules.json')
+    dashboard_uri = URI.parse("#{@host}/training_modules.json")
     response = Net::HTTP.get_response(dashboard_uri)
     return [] unless response.is_a?(Net::HTTPSuccess)
 
diff --git a/lib/analytics/tagged_courses_csv_builder.rb b/lib/analytics/tagged_courses_csv_builder.rb
index d7fcd03cd3..e3d53e22d8 100644
--- a/lib/analytics/tagged_courses_csv_builder.rb
+++ b/lib/analytics/tagged_courses_csv_builder.rb
@@ -24,7 +24,7 @@ def initialize(tag)
 
   def row(course) # rubocop:disable Metrics/AbcSize
     row = [course.title]
-    row << (course.school + '/' + course.term)
+    row << ("#{course.school}/#{course.term}")
     row << (@wiki_experts.find { |user| user.course_id == course.id }&.user&.username || 'N/A')
     row << course.courses_users.where(role: 1).first&.real_name
     row << course.recent_revision_count
diff --git a/lib/default_campaign_update.rb b/lib/default_campaign_update.rb
index f1344289c4..f0cc319b14 100644
--- a/lib/default_campaign_update.rb
+++ b/lib/default_campaign_update.rb
@@ -14,6 +14,6 @@ def current_term
     month = Time.zone.today.month
     # Determine if it's spring or fall semester based on academic calendar
     semester = month.between?(1, 6) ? 'spring' : 'fall'
-    semester + '_' + year.to_s
+    "#{semester}_#{year}"
   end
 end
diff --git a/lib/errors/rescue_development_errors.rb b/lib/errors/rescue_development_errors.rb
index c80ef0f231..cbd745dac4 100644
--- a/lib/errors/rescue_development_errors.rb
+++ b/lib/errors/rescue_development_errors.rb
@@ -15,7 +15,7 @@ def self.included(base)
     def self.rescue_from_rev_manifest(base)
       base.rescue_from ActionView::Template::Error do |e|
         raise e unless /rev-manifest.json/.match?(e.message)
-        explanation = '<p><code>' + String.new(e.message) + '</p></code>'
+        explanation = "<p><code>#{String.new(e.message)}</p></code>"
         explanation << REV_MANIFEST_EXPLANATION
 
         render plain: explanation,
diff --git a/lib/pagepile_api.rb b/lib/pagepile_api.rb
index f1cd3faa75..0e839fc417 100644
--- a/lib/pagepile_api.rb
+++ b/lib/pagepile_api.rb
@@ -56,7 +56,7 @@ def query_url
 
   def pagepile
     conn = Faraday.new(url: 'https://pagepile.toolforge.org')
-    conn.headers['User-Agent'] = ENV['dashboard_url'] + ' ' + Rails.env
+    conn.headers['User-Agent'] = "#{ENV['dashboard_url']} #{Rails.env}"
     conn
   end
 
diff --git a/lib/petscan_api.rb b/lib/petscan_api.rb
index 3dcddfb12d..168713e605 100644
--- a/lib/petscan_api.rb
+++ b/lib/petscan_api.rb
@@ -43,7 +43,7 @@ def query_url(psid)
 
   def petscan
     conn = Faraday.new(url: 'https://petscan.wmcloud.org')
-    conn.headers['User-Agent'] = ENV['dashboard_url'] + ' ' + Rails.env
+    conn.headers['User-Agent'] = "#{ENV['dashboard_url']} #{Rails.env}"
     conn
   end
 
diff --git a/lib/training/wiki_training_loader.rb b/lib/training/wiki_training_loader.rb
index 61c2edaa10..da5fb0a0c1 100644
--- a/lib/training/wiki_training_loader.rb
+++ b/lib/training/wiki_training_loader.rb
@@ -116,7 +116,7 @@ def translated_pages(base_page:, base_page_wikitext:)
     return [] unless response
     translations = []
     response.data['messagegroupstats'].each do |language|
-      translations << (base_page + '/' + language['code']) if any_translations?(language)
+      translations << ("#{base_page}/#{language['code']}") if any_translations?(language)
     end
     return translations
   end
diff --git a/lib/wiki_course_edits.rb b/lib/wiki_course_edits.rb
index 0b00d61022..c681e9cab5 100644
--- a/lib/wiki_course_edits.rb
+++ b/lib/wiki_course_edits.rb
@@ -157,7 +157,7 @@ def add_template_to_user_page
     return if initial_page_content.include?(template)
 
     summary = @generator.enrollment_summary
-    new_line_template = template + "\n"
+    new_line_template = "#{template}\n"
     @wiki_editor.add_to_page_top(user_page, @current_user, new_line_template, summary)
   end
 
@@ -170,7 +170,7 @@ def add_template_to_user_talk_page
     return if initial_page_content.include?(talk_template)
 
     talk_summary = "adding {{#{template_name(@templates, 'user_talk')}}}"
-    new_line_template = talk_template + "\n"
+    new_line_template = "#{talk_template}\n"
     @wiki_editor.add_to_page_top(talk_page, @current_user, new_line_template, talk_summary)
   end
 
diff --git a/lib/wiki_course_output.rb b/lib/wiki_course_output.rb
index 1e76ab17c0..37b6f04925 100644
--- a/lib/wiki_course_output.rb
+++ b/lib/wiki_course_output.rb
@@ -44,7 +44,7 @@ def translate_course_to_wikitext
 
   def course_details_and_description
     description = Wikitext.markdown_to_mediawiki(@course.description)
-    course_details + "\r" + description
+    "#{course_details}\r#{description}"
   end
 
   def course_details # rubocop:disable Metrics/MethodLength
diff --git a/lib/wiki_edits.rb b/lib/wiki_edits.rb
index dea4f0d789..40731a4375 100644
--- a/lib/wiki_edits.rb
+++ b/lib/wiki_edits.rb
@@ -24,7 +24,7 @@ def oauth_credentials_valid?(current_user)
   def notify_untrained(course, current_user)
     untrained_users = course.students_with_overdue_training
     training_link = "https://#{ENV['dashboard_url']}/training/students"
-    signed_text = I18n.t('wiki_edits.notify_overdue.message', link: training_link) + ' --~~~~'
+    signed_text = "#{I18n.t('wiki_edits.notify_overdue.message', link: training_link)} --~~~~"
 
     message = { sectiontitle: I18n.t('wiki_edits.notify_overdue.header'),
                 text: signed_text,
diff --git a/lib/wikitext.rb b/lib/wikitext.rb
index 290ef41321..4a637e27f9 100644
--- a/lib/wikitext.rb
+++ b/lib/wikitext.rb
@@ -71,7 +71,7 @@ def self.assignments_to_wikilinks(assignments, home_wiki)
     formatted_titles = assignments.map do |assignment|
       format_assignment_title(assignment, home_wiki)
     end
-    wikitext = '[[' + formatted_titles.join(']], [[') + ']]'
+    wikitext = "[[#{formatted_titles.join(']], [[')}]]"
     wikitext
   end
 
@@ -90,7 +90,7 @@ def self.format_assignment_title(assignment, home_wiki)
     # If the project is different, a project prefix is also necessary.
     project_prefix = project == home_wiki.project ? '' : ":#{project}"
 
-    (INTERWIKI_PREFIXES[project_prefix] || project_prefix) + language_prefix + ':' + title
+    "#{INTERWIKI_PREFIXES[project_prefix] || project_prefix}#{language_prefix}:#{title}"
   end
 
   # converts page title to a format suitable for on-wiki use
diff --git a/spec/features/surveys_spec.rb b/spec/features/surveys_spec.rb
index e38d393eb9..1682059292 100644
--- a/spec/features/surveys_spec.rb
+++ b/spec/features/surveys_spec.rb
@@ -248,7 +248,7 @@
       expect(SurveyNotification.last.completed).to eq(true)
 
       expect(Survey.last.to_csv).to match('username,') # beginning of header
-      expect(Survey.last.to_csv).to match(@instructor.username + ',') # beginning of response row
+      expect(Survey.last.to_csv).to match("#{@instructor.username},") # beginning of response row
     end
 
     it 'loads a question group preview' do
diff --git a/spec/lib/analytics/course_wikidata_csv_builder_spec.rb b/spec/lib/analytics/course_wikidata_csv_builder_spec.rb
index 9ffb8e6135..f0c9ccca37 100644
--- a/spec/lib/analytics/course_wikidata_csv_builder_spec.rb
+++ b/spec/lib/analytics/course_wikidata_csv_builder_spec.rb
@@ -28,7 +28,7 @@
 
     it 'generates csv data' do
       expect(builder.generate_csv.lines.first).to start_with('course name,claims created')
-      expect(builder.generate_csv.lines.last).to start_with(course.title + ',2')
+      expect(builder.generate_csv.lines.last).to start_with("#{course.title},2")
       expect(builder.generate_csv.lines.count).to eq 2
     end
   end
diff --git a/spec/lib/importers/user_importer_spec.rb b/spec/lib/importers/user_importer_spec.rb
index fdb4d596d7..3ead757924 100644
--- a/spec/lib/importers/user_importer_spec.rb
+++ b/spec/lib/importers/user_importer_spec.rb
@@ -132,15 +132,15 @@
 
     it 'removes invisible left-to-right and right-to-left marks from start or end of username' do
       VCR.use_cassette 'user/new_from_username_with_ltr' do
-        username = 'Jashan1994' + 8206.chr + 8206.chr
+        username = "Jashan1994#{8206.chr}#{8206.chr}"
         user = described_class.new_from_username(username)
         expect(user.username).to eq('Jashan1994')
 
-        username = 8206.chr + 'Jashan1994'
+        username = "#{8206.chr}Jashan1994"
         user = described_class.new_from_username(username)
         expect(user.username).to eq('Jashan1994')
 
-        username = 8207.chr + 'Ofrit Assaf'
+        username = "#{8207.chr}Ofrit Assaf"
         user = described_class.new_from_username(username)
         expect(user.username).to eq('Ofrit Assaf')
       end
diff --git a/spec/lib/wiki_assignment_output_spec.rb b/spec/lib/wiki_assignment_output_spec.rb
index feceb5236f..48f9243164 100644
--- a/spec/lib/wiki_assignment_output_spec.rb
+++ b/spec/lib/wiki_assignment_output_spec.rb
@@ -197,7 +197,7 @@
         output = wiki_assignment_output
                  .build_assignment_page_content(assignment_tag,
                                                 initial_talk_page_content)
-        expected_output = assignment_tag + "\n\n" + initial_talk_page_content
+        expected_output = "#{assignment_tag}\n\n#{initial_talk_page_content}"
         expect(output).to eq(expected_output)
       end
 
@@ -209,7 +209,7 @@
         output = wiki_assignment_output
                  .build_assignment_page_content(assignment_tag,
                                                 initial_talk_page_content)
-        expected_output = talk_page_templates + assignment_tag + "\n" + additional_talk_content
+        expected_output = "#{talk_page_templates}#{assignment_tag}\n#{additional_talk_content}"
         expect(output).to eq(expected_output)
       end
 
@@ -254,7 +254,7 @@
         output = wiki_assignment_output
                  .build_assignment_page_content(assignment_tag,
                                                 initial_talk_page_content)
-        expected_output = initial_talk_page_content + assignment_tag + "\n"
+        expected_output = "#{initial_talk_page_content}#{assignment_tag}\n"
         expect(output).to eq(expected_output)
       end
     end
diff --git a/spec/mailers/course_approval_mailer_spec.rb b/spec/mailers/course_approval_mailer_spec.rb
index 48d959f5e2..ee899414c2 100644
--- a/spec/mailers/course_approval_mailer_spec.rb
+++ b/spec/mailers/course_approval_mailer_spec.rb
@@ -11,7 +11,7 @@
 
     it 'delivers an email with an enrollment link' do
       allow(Features).to receive(:email?).and_return(true)
-      expect(mail.html_part.body).to include(escaped_slug(course.slug) + '?enroll=')
+      expect(mail.html_part.body).to include("#{escaped_slug(course.slug)}?enroll=")
       expect(mail.to).to eq([instructor.email])
     end
   end
diff --git a/spec/services/copy_course_spec.rb b/spec/services/copy_course_spec.rb
index 7186f4eb99..2b42b42b04 100644
--- a/spec/services/copy_course_spec.rb
+++ b/spec/services/copy_course_spec.rb
@@ -12,11 +12,11 @@
   let(:existent_prod_course_slug) do
     'University_of_South_Carolina/Invertebrate_Zoology_(COPIED_FROM_Spring_2022)'
   end
-  let(:course_url) { url_base + existent_prod_course_slug + '/course.json' }
-  let(:categories_url) { url_base + existent_prod_course_slug + '/categories.json' }
-  let(:users_url) { url_base + existent_prod_course_slug + '/users.json' }
-  let(:timeline_url) { url_base + existent_prod_course_slug + '/timeline.json' }
-  let(:training_modules_url) { @selected_dashboard + '/training_modules.json' }
+  let(:course_url) { "#{url_base}#{existent_prod_course_slug}/course.json" }
+  let(:categories_url) { "#{url_base}#{existent_prod_course_slug}/categories.json" }
+  let(:users_url) { "#{url_base}#{existent_prod_course_slug}/users.json" }
+  let(:timeline_url) { "#{url_base}#{existent_prod_course_slug}/timeline.json" }
+  let(:training_modules_url) { "#{@selected_dashboard}/training_modules.json" }
   let(:course_response_body) do
     '{
       "course": {