diff --git a/.rubocop.yml b/.rubocop.yml
index e5b26bccc9c..ba420f09b6e 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -99,6 +99,9 @@ Style/BracesAroundHashParameters:
   Enabled: false
 Style/ClassAndModuleChildren:
   Enabled: false
+Style/FrozenStringLiteralComment:
+  Enabled: true
+  EnforcedStyle: always
 Style/Documentation:
   Enabled: false
   Exclude:
diff --git a/Gemfile b/Gemfile
index 0306c71afc1..0dcb47767d4 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source "https://rubygems.org"
 gemspec :name => "jekyll"
 
diff --git a/Rakefile b/Rakefile
index c80324aba5d..a7d50088d93 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "rubygems"
 require "rake"
 require "rdoc"
diff --git a/docs/_docs/history.md b/docs/_docs/history.md
index e5832bf0998..725321bddae 100644
--- a/docs/_docs/history.md
+++ b/docs/_docs/history.md
@@ -27,7 +27,7 @@ note: This file is autogenerated. Edit /History.markdown instead.
 - add plugins for multiple page pagination ([#6055]({{ site.repository }}/issues/6055))
 - Update minimum Ruby version in installation.md ([#6164]({{ site.repository }}/issues/6164))
 - [docs] Add information about finding a collection in `site.collections` ([#6165]({{ site.repository }}/issues/6165))
-- Add {%raw%} to Liquid example on site ([#6179]({{ site.repository }}/issues/6179))
+- Add {% raw %}`{% raw %}`{% endraw %} to Liquid example on site ([#6179]({{ site.repository }}/issues/6179))
 - Added improved Pug plugin - removed 404 Jade plugin ([#6174]({{ site.repository }}/issues/6174))
 - Linking the link ([#6210]({{ site.repository }}/issues/6210))
 - Small correction in documentation for includes ([#6193]({{ site.repository }}/issues/6193))
diff --git a/features/step_definitions.rb b/features/step_definitions.rb
index c22adb48667..29900491989 100644
--- a/features/step_definitions.rb
+++ b/features/step_definitions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 Before do
   FileUtils.rm_rf(Paths.test_dir) if Paths.test_dir.exist?
   FileUtils.mkdir_p(Paths.test_dir) unless Paths.test_dir.directory?
diff --git a/features/support/formatter.rb b/features/support/formatter.rb
index 79d1466480f..745c74ec905 100644
--- a/features/support/formatter.rb
+++ b/features/support/formatter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "fileutils"
 require "colorator"
 require "cucumber/formatter/console"
diff --git a/features/support/helpers.rb b/features/support/helpers.rb
index 118dd9cf925..13a8b78cf2d 100644
--- a/features/support/helpers.rb
+++ b/features/support/helpers.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "fileutils"
 require "jekyll"
 require "time"
@@ -107,7 +109,7 @@ def run_in_shell(*args)
 
   File.write(Paths.status_file, p.exitstatus)
   File.open(Paths.output_file, "wb") do |f|
-    f.puts "$ " << args.join(" ")
+    f.puts "$ #{args.join(" ")}"
     f.puts output
     f.puts "EXIT STATUS: #{p.exitstatus}"
   end
diff --git a/jekyll.gemspec b/jekyll.gemspec
index 5ec2e9a25f6..87031a8000c 100644
--- a/jekyll.gemspec
+++ b/jekyll.gemspec
@@ -1,4 +1,5 @@
 # coding: utf-8
+# frozen_string_literal: true
 
 lib = File.expand_path("lib", __dir__)
 $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
diff --git a/lib/jekyll.rb b/lib/jekyll.rb
index 5e5923c2bd1..fb5db3d43e1 100644
--- a/lib/jekyll.rb
+++ b/lib/jekyll.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 $LOAD_PATH.unshift __dir__ # For use/testing when no gem is installed
 
 # Require all of the Ruby files in the given directory.
@@ -162,8 +164,9 @@ def sites
     def sanitized_path(base_directory, questionable_path)
       return base_directory if base_directory.eql?(questionable_path)
 
-      questionable_path.insert(0, "/") if questionable_path.start_with?("~")
-      clean_path = File.expand_path(questionable_path, "/")
+      clean_path = questionable_path.dup
+      clean_path.insert(0, "/") if clean_path.start_with?("~")
+      clean_path = File.expand_path(clean_path, "/")
 
       return clean_path if clean_path.eql?(base_directory)
 
diff --git a/lib/jekyll/cleaner.rb b/lib/jekyll/cleaner.rb
index db8a9180f94..fee6418a99c 100644
--- a/lib/jekyll/cleaner.rb
+++ b/lib/jekyll/cleaner.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "set"
 
 module Jekyll
diff --git a/lib/jekyll/collection.rb b/lib/jekyll/collection.rb
index f839915f599..ebafea38f97 100644
--- a/lib/jekyll/collection.rb
+++ b/lib/jekyll/collection.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Collection
     attr_reader :site, :label, :metadata
diff --git a/lib/jekyll/command.rb b/lib/jekyll/command.rb
index f9f243dd9e6..7de98e76ea8 100644
--- a/lib/jekyll/command.rb
+++ b/lib/jekyll/command.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Command
     class << self
diff --git a/lib/jekyll/commands/build.rb b/lib/jekyll/commands/build.rb
index 3cea607cbd0..1bd176b8be4 100644
--- a/lib/jekyll/commands/build.rb
+++ b/lib/jekyll/commands/build.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Commands
     class Build < Command
diff --git a/lib/jekyll/commands/clean.rb b/lib/jekyll/commands/clean.rb
index 3a44d59683e..1c3e40bf6c4 100644
--- a/lib/jekyll/commands/clean.rb
+++ b/lib/jekyll/commands/clean.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Commands
     class Clean < Command
diff --git a/lib/jekyll/commands/doctor.rb b/lib/jekyll/commands/doctor.rb
index 5c235dac132..1ef87e714d5 100644
--- a/lib/jekyll/commands/doctor.rb
+++ b/lib/jekyll/commands/doctor.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "addressable/uri"
 
 module Jekyll
diff --git a/lib/jekyll/commands/help.rb b/lib/jekyll/commands/help.rb
index b4f136bf3e5..42a8017ae8a 100644
--- a/lib/jekyll/commands/help.rb
+++ b/lib/jekyll/commands/help.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Commands
     class Help < Command
diff --git a/lib/jekyll/commands/new.rb b/lib/jekyll/commands/new.rb
index d1aeb5a0281..b1c8bb0bc4b 100644
--- a/lib/jekyll/commands/new.rb
+++ b/lib/jekyll/commands/new.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "erb"
 
 module Jekyll
diff --git a/lib/jekyll/commands/new_theme.rb b/lib/jekyll/commands/new_theme.rb
index 65125d58d50..c55e68127d8 100644
--- a/lib/jekyll/commands/new_theme.rb
+++ b/lib/jekyll/commands/new_theme.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "erb"
 
 class Jekyll::Commands::NewTheme < Jekyll::Command
diff --git a/lib/jekyll/commands/serve.rb b/lib/jekyll/commands/serve.rb
index 4bc9eaf0da8..53973b66cb4 100644
--- a/lib/jekyll/commands/serve.rb
+++ b/lib/jekyll/commands/serve.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Commands
     class Serve < Command
diff --git a/lib/jekyll/commands/serve/servlet.rb b/lib/jekyll/commands/serve/servlet.rb
index 2e20ace81d5..b661940c30a 100644
--- a/lib/jekyll/commands/serve/servlet.rb
+++ b/lib/jekyll/commands/serve/servlet.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "webrick"
 
 module Jekyll
diff --git a/lib/jekyll/configuration.rb b/lib/jekyll/configuration.rb
index ec8e2a22dc0..2931cba4500 100644
--- a/lib/jekyll/configuration.rb
+++ b/lib/jekyll/configuration.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   class Configuration < Hash
diff --git a/lib/jekyll/converter.rb b/lib/jekyll/converter.rb
index b7fa0091cb3..3cb74de2123 100644
--- a/lib/jekyll/converter.rb
+++ b/lib/jekyll/converter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Converter < Plugin
     # Public: Get or set the highlighter prefix. When an argument is specified,
diff --git a/lib/jekyll/converters/identity.rb b/lib/jekyll/converters/identity.rb
index 9574769d1a9..2296aff1966 100644
--- a/lib/jekyll/converters/identity.rb
+++ b/lib/jekyll/converters/identity.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Converters
     class Identity < Converter
diff --git a/lib/jekyll/converters/markdown.rb b/lib/jekyll/converters/markdown.rb
index c718d539b7c..3e53992104d 100644
--- a/lib/jekyll/converters/markdown.rb
+++ b/lib/jekyll/converters/markdown.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Converters
     class Markdown < Converter
diff --git a/lib/jekyll/converters/markdown/rdiscount_parser.rb b/lib/jekyll/converters/markdown/rdiscount_parser.rb
index f1679e796c4..654a3a6d0ed 100644
--- a/lib/jekyll/converters/markdown/rdiscount_parser.rb
+++ b/lib/jekyll/converters/markdown/rdiscount_parser.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Converters
     class Markdown
diff --git a/lib/jekyll/converters/markdown/redcarpet_parser.rb b/lib/jekyll/converters/markdown/redcarpet_parser.rb
index aa170feb3b7..fae09621da2 100644
--- a/lib/jekyll/converters/markdown/redcarpet_parser.rb
+++ b/lib/jekyll/converters/markdown/redcarpet_parser.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Jekyll::Converters::Markdown::RedcarpetParser
   module CommonMethods
     def add_code_tags(code, lang)
@@ -48,9 +50,7 @@ module WithRouge
     def block_code(code, lang)
       code = "<pre>#{super}</pre>"
 
-      output = "<div class=\"highlight\">"
-      output << add_code_tags(code, lang)
-      output << "</div>"
+      "<div class=\"highlight\">#{add_code_tags(code, lang)}</div>"
     end
 
     protected
diff --git a/lib/jekyll/converters/smartypants.rb b/lib/jekyll/converters/smartypants.rb
index d1bc81039a1..37fecb12172 100644
--- a/lib/jekyll/converters/smartypants.rb
+++ b/lib/jekyll/converters/smartypants.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Kramdown::Parser::SmartyPants < Kramdown::Parser::Kramdown
   def initialize(source, options)
     super
diff --git a/lib/jekyll/convertible.rb b/lib/jekyll/convertible.rb
index 74125f09b1d..aea33fdcb86 100644
--- a/lib/jekyll/convertible.rb
+++ b/lib/jekyll/convertible.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 require "set"
 
diff --git a/lib/jekyll/deprecator.rb b/lib/jekyll/deprecator.rb
index ca2b8b3f74a..327358c2d4f 100644
--- a/lib/jekyll/deprecator.rb
+++ b/lib/jekyll/deprecator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Deprecator
     extend self
diff --git a/lib/jekyll/document.rb b/lib/jekyll/document.rb
index 8634082c4d9..b6493f3c075 100644
--- a/lib/jekyll/document.rb
+++ b/lib/jekyll/document.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   class Document
diff --git a/lib/jekyll/drops/collection_drop.rb b/lib/jekyll/drops/collection_drop.rb
index 5f5025b1f2d..2c9c01320ea 100644
--- a/lib/jekyll/drops/collection_drop.rb
+++ b/lib/jekyll/drops/collection_drop.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   module Drops
diff --git a/lib/jekyll/drops/document_drop.rb b/lib/jekyll/drops/document_drop.rb
index ed851821eb1..7796980c7a4 100644
--- a/lib/jekyll/drops/document_drop.rb
+++ b/lib/jekyll/drops/document_drop.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   module Drops
diff --git a/lib/jekyll/drops/drop.rb b/lib/jekyll/drops/drop.rb
index 6227213e4dd..1ded11eb7d2 100644
--- a/lib/jekyll/drops/drop.rb
+++ b/lib/jekyll/drops/drop.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   module Drops
diff --git a/lib/jekyll/drops/excerpt_drop.rb b/lib/jekyll/drops/excerpt_drop.rb
index 5d61aeb1b2d..06f8ae7d016 100644
--- a/lib/jekyll/drops/excerpt_drop.rb
+++ b/lib/jekyll/drops/excerpt_drop.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   module Drops
diff --git a/lib/jekyll/drops/jekyll_drop.rb b/lib/jekyll/drops/jekyll_drop.rb
index e3d2eb38d52..1686da418f1 100644
--- a/lib/jekyll/drops/jekyll_drop.rb
+++ b/lib/jekyll/drops/jekyll_drop.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   module Drops
diff --git a/lib/jekyll/drops/site_drop.rb b/lib/jekyll/drops/site_drop.rb
index 97b41806444..cb4a007eb15 100644
--- a/lib/jekyll/drops/site_drop.rb
+++ b/lib/jekyll/drops/site_drop.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   module Drops
diff --git a/lib/jekyll/drops/static_file_drop.rb b/lib/jekyll/drops/static_file_drop.rb
index e0af2f09ed1..f855cf33629 100644
--- a/lib/jekyll/drops/static_file_drop.rb
+++ b/lib/jekyll/drops/static_file_drop.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Drops
     class StaticFileDrop < Drop
diff --git a/lib/jekyll/drops/unified_payload_drop.rb b/lib/jekyll/drops/unified_payload_drop.rb
index b642bda2620..833443a46f9 100644
--- a/lib/jekyll/drops/unified_payload_drop.rb
+++ b/lib/jekyll/drops/unified_payload_drop.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   module Drops
diff --git a/lib/jekyll/drops/url_drop.rb b/lib/jekyll/drops/url_drop.rb
index 5c97190da59..e67d24d47b8 100644
--- a/lib/jekyll/drops/url_drop.rb
+++ b/lib/jekyll/drops/url_drop.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   module Drops
diff --git a/lib/jekyll/entry_filter.rb b/lib/jekyll/entry_filter.rb
index f4425037afc..019133195d3 100644
--- a/lib/jekyll/entry_filter.rb
+++ b/lib/jekyll/entry_filter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class EntryFilter
     attr_reader :site
diff --git a/lib/jekyll/errors.rb b/lib/jekyll/errors.rb
index 95aa04b4ccd..8d659e8d285 100644
--- a/lib/jekyll/errors.rb
+++ b/lib/jekyll/errors.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Errors
     FatalException = Class.new(::RuntimeError)
diff --git a/lib/jekyll/excerpt.rb b/lib/jekyll/excerpt.rb
index 61344e7964b..7adfec9861c 100644
--- a/lib/jekyll/excerpt.rb
+++ b/lib/jekyll/excerpt.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Excerpt
     extend Forwardable
@@ -117,7 +119,7 @@ def extract_excerpt(doc_content)
       if tail.empty?
         head
       else
-        "" << head << "\n\n" << tail.scan(%r!^ {0,3}\[[^\]]+\]:.+$!).join("\n")
+        head.to_s.dup << "\n\n" << tail.scan(%r!^ {0,3}\[[^\]]+\]:.+$!).join("\n")
       end
     end
   end
diff --git a/lib/jekyll/external.rb b/lib/jekyll/external.rb
index bdefc798ae8..0a65dfad058 100644
--- a/lib/jekyll/external.rb
+++ b/lib/jekyll/external.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module External
     class << self
diff --git a/lib/jekyll/filters.rb b/lib/jekyll/filters.rb
index e15cf7c66dd..35ed4d9f63e 100644
--- a/lib/jekyll/filters.rb
+++ b/lib/jekyll/filters.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "addressable/uri"
 require "json"
 require "date"
diff --git a/lib/jekyll/filters/grouping_filters.rb b/lib/jekyll/filters/grouping_filters.rb
index c1029256106..4086bbe9854 100644
--- a/lib/jekyll/filters/grouping_filters.rb
+++ b/lib/jekyll/filters/grouping_filters.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Filters
     module GroupingFilters
diff --git a/lib/jekyll/filters/url_filters.rb b/lib/jekyll/filters/url_filters.rb
index 6ededc956d1..5bae1b1794e 100644
--- a/lib/jekyll/filters/url_filters.rb
+++ b/lib/jekyll/filters/url_filters.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "addressable/uri"
 
 module Jekyll
diff --git a/lib/jekyll/frontmatter_defaults.rb b/lib/jekyll/frontmatter_defaults.rb
index 7cbfa358677..fc1bcc2d867 100644
--- a/lib/jekyll/frontmatter_defaults.rb
+++ b/lib/jekyll/frontmatter_defaults.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   # This class handles custom defaults for YAML frontmatter settings.
   # These are set in _config.yml and apply both to internal use (e.g. layout)
diff --git a/lib/jekyll/generator.rb b/lib/jekyll/generator.rb
index bf7c0f19aba..649715f840c 100644
--- a/lib/jekyll/generator.rb
+++ b/lib/jekyll/generator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   Generator = Class.new(Plugin)
 end
diff --git a/lib/jekyll/hooks.rb b/lib/jekyll/hooks.rb
index 241dce3a7f1..8007edff59c 100644
--- a/lib/jekyll/hooks.rb
+++ b/lib/jekyll/hooks.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Hooks
     DEFAULT_PRIORITY = 20
diff --git a/lib/jekyll/layout.rb b/lib/jekyll/layout.rb
index 3a08ad0d3be..f62fec08be2 100644
--- a/lib/jekyll/layout.rb
+++ b/lib/jekyll/layout.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Layout
     include Convertible
diff --git a/lib/jekyll/liquid_extensions.rb b/lib/jekyll/liquid_extensions.rb
index 5ba7dd8e79f..4551ac19bbd 100644
--- a/lib/jekyll/liquid_extensions.rb
+++ b/lib/jekyll/liquid_extensions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module LiquidExtensions
 
diff --git a/lib/jekyll/liquid_renderer.rb b/lib/jekyll/liquid_renderer.rb
index 919930ef8b0..2e15dbc6dcd 100644
--- a/lib/jekyll/liquid_renderer.rb
+++ b/lib/jekyll/liquid_renderer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "jekyll/liquid_renderer/file"
 require "jekyll/liquid_renderer/table"
 
diff --git a/lib/jekyll/liquid_renderer/file.rb b/lib/jekyll/liquid_renderer/file.rb
index eec8c7b52a8..574bbd31300 100644
--- a/lib/jekyll/liquid_renderer/file.rb
+++ b/lib/jekyll/liquid_renderer/file.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class LiquidRenderer
     class File
diff --git a/lib/jekyll/liquid_renderer/table.rb b/lib/jekyll/liquid_renderer/table.rb
index aab7fdf7845..7aa2e49ee4e 100644
--- a/lib/jekyll/liquid_renderer/table.rb
+++ b/lib/jekyll/liquid_renderer/table.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class LiquidRenderer::Table
     def initialize(stats)
@@ -13,7 +15,7 @@ def to_s(n = 50)
     private
 
     def generate_table(data, widths)
-      str = "\n"
+      str = String.new("\n")
 
       table_head = data.shift
       str << generate_row(table_head, widths)
@@ -28,7 +30,7 @@ def generate_table(data, widths)
     end
 
     def generate_table_head_border(row_data, widths)
-      str = ""
+      str = String.new("")
 
       row_data.each_index do |cell_index|
         str << "-" * widths[cell_index]
@@ -40,7 +42,7 @@ def generate_table_head_border(row_data, widths)
     end
 
     def generate_row(row_data, widths)
-      str = ""
+      str = String.new("")
 
       row_data.each_with_index do |cell_data, cell_index|
         str << if cell_index.zero?
diff --git a/lib/jekyll/log_adapter.rb b/lib/jekyll/log_adapter.rb
index 965f3295702..ec33b4d90d8 100644
--- a/lib/jekyll/log_adapter.rb
+++ b/lib/jekyll/log_adapter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class LogAdapter
     attr_reader :writer, :messages
diff --git a/lib/jekyll/mime.types b/lib/jekyll/mime.types
index 15828b91c4c..1aefbb586d3 100644
--- a/lib/jekyll/mime.types
+++ b/lib/jekyll/mime.types
@@ -14,7 +14,7 @@ application/cdmi-domain                                                   cdmid
 application/cdmi-object                                                   cdmio
 application/cdmi-queue                                                    cdmiq
 application/cu-seeme                                                      cu
-application/dash+xml                                                      mdp
+application/dash+xml                                                      mpd
 application/davmount+xml                                                  davmount
 application/docbook+xml                                                   dbk
 application/dssc+der                                                      dssc
@@ -26,9 +26,11 @@ application/exi                                                           exi
 application/font-tdpfr                                                    pfr
 application/font-woff                                                     woff
 application/font-woff2                                                    woff2
+application/geo+json                                                      geojson
 application/gml+xml                                                       gml
 application/gpx+xml                                                       gpx
 application/gxf                                                           gxf
+application/gzip                                                          gz
 application/hyperstudio                                                   stk
 application/inkml+xml                                                     ink inkml
 application/ipfix                                                         ipfix
@@ -142,6 +144,7 @@ application/vnd.anser-web-funds-transfer-initiation                       fti
 application/vnd.antix.game-component                                      atx
 application/vnd.apple.installer+xml                                       mpkg
 application/vnd.apple.mpegurl                                             m3u8
+application/vnd.apple.pkpass                                              pkpass
 application/vnd.aristanetworks.swi                                        swi
 application/vnd.astraea-software.iota                                     iota
 application/vnd.audiograph                                                aep
@@ -220,6 +223,9 @@ application/vnd.geonext                                                   gxt
 application/vnd.geoplan                                                   g2w
 application/vnd.geospace                                                  g3w
 application/vnd.gmx                                                       gmx
+application/vnd.google-apps.document                                      gdoc
+application/vnd.google-apps.presentation                                  gslides
+application/vnd.google-apps.spreadsheet                                   gsheet
 application/vnd.google-earth.kml+xml                                      kml
 application/vnd.google-earth.kmz                                          kmz
 application/vnd.grafeq                                                    gqf gqs
@@ -317,6 +323,7 @@ application/vnd.ms-htmlhelp                                               chm
 application/vnd.ms-ims                                                    ims
 application/vnd.ms-lrm                                                    lrm
 application/vnd.ms-officetheme                                            thmx
+application/vnd.ms-outlook                                                msg
 application/vnd.ms-pki.seccat                                             cat
 application/vnd.ms-pki.stl                                                stl
 application/vnd.ms-powerpoint                                             ppt pps pot
@@ -422,6 +429,7 @@ application/vnd.stardivision.writer                                       sdw vo
 application/vnd.stardivision.writer-global                                sgl
 application/vnd.stepmania.package                                         smzip
 application/vnd.stepmania.stepchart                                       sm
+application/vnd.sun.wadl+xml                                              wadl
 application/vnd.sun.xml.calc                                              sxc
 application/vnd.sun.xml.calc.template                                     stc
 application/vnd.sun.xml.draw                                              sxd
@@ -594,7 +602,7 @@ application/xaml+xml                                                      xaml
 application/xcap-diff+xml                                                 xdf
 application/xenc+xml                                                      xenc
 application/xhtml+xml                                                     xhtml xht
-application/xml                                                           xml xsl xsd
+application/xml                                                           xml xsl xsd rng
 application/xml-dtd                                                       dtd
 application/xop+xml                                                       xop
 application/xproc+xml                                                     xpl
@@ -604,11 +612,13 @@ application/xv+xml                                                        mxml x
 application/yang                                                          yang
 application/yin+xml                                                       yin
 application/zip                                                           zip
+audio/3gpp                                                                3gpp
 audio/adpcm                                                               adp
 audio/basic                                                               au snd
 audio/midi                                                                mid midi kar rmi
-audio/mp4                                                                 mp4a m4a
-audio/mpeg                                                                mpga mp2 mp2a mp3 m2a m3a
+audio/mp3                                                                 mp3
+audio/mp4                                                                 m4a mp4a
+audio/mpeg                                                                mpga mp2 mp2a m2a m3a
 audio/ogg                                                                 oga ogg spx
 audio/s3m                                                                 s3m
 audio/silk                                                                sil
@@ -642,6 +652,7 @@ chemical/x-cmdf                                                           cmdf
 chemical/x-cml                                                            cml
 chemical/x-csml                                                           csml
 chemical/x-xyz                                                            xyz
+image/apng                                                                apng
 image/bmp                                                                 bmp
 image/cgm                                                                 cgm
 image/g3fax                                                               g3
@@ -690,6 +701,8 @@ image/x-xbitmap                                                           xbm
 image/x-xpixmap                                                           xpm
 image/x-xwindowdump                                                       xwd
 message/rfc822                                                            eml mime
+model/gltf+json                                                           gltf
+model/gltf-binary                                                         glb
 model/iges                                                                igs iges
 model/mesh                                                                msh mesh silo
 model/vnd.collada+xml                                                     dae
@@ -712,12 +725,14 @@ text/html                                                                 html h
 text/jade                                                                 jade
 text/jsx                                                                  jsx
 text/less                                                                 less
+text/markdown                                                             markdown md
 text/mathml                                                               mml
 text/n3                                                                   n3
 text/plain                                                                txt text conf def list log in ini
 text/prs.lines.tag                                                        dsc
 text/richtext                                                             rtx
 text/sgml                                                                 sgml sgm
+text/slim                                                                 slim slm
 text/stylus                                                               stylus styl
 text/tab-separated-values                                                 tsv
 text/troff                                                                t tr roff man me ms
@@ -744,7 +759,7 @@ text/x-fortran                                                            f for
 text/x-handlebars-template                                                hbs
 text/x-java-source                                                        java
 text/x-lua                                                                lua
-text/x-markdown                                                           markdown md mkd
+text/x-markdown                                                           mkd
 text/x-nfo                                                                nfo
 text/x-opml                                                               opml
 text/x-pascal                                                             p pas
@@ -753,11 +768,12 @@ text/x-sass                                                               sass
 text/x-scss                                                               scss
 text/x-setext                                                             etx
 text/x-sfv                                                                sfv
+text/x-suse-ymp                                                           ymp
 text/x-uuencode                                                           uu
 text/x-vcalendar                                                          vcs
 text/x-vcard                                                              vcf
 text/yaml                                                                 yaml yml
-video/3gpp                                                                3gp 3gpp
+video/3gpp                                                                3gp
 video/3gpp2                                                               3g2
 video/h261                                                                h261
 video/h263                                                                h263
diff --git a/lib/jekyll/page.rb b/lib/jekyll/page.rb
index 02c6cfae9f1..3b3d9353879 100644
--- a/lib/jekyll/page.rb
+++ b/lib/jekyll/page.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Page
     include Convertible
diff --git a/lib/jekyll/plugin.rb b/lib/jekyll/plugin.rb
index b6e5023d80e..2a9dbeed41b 100644
--- a/lib/jekyll/plugin.rb
+++ b/lib/jekyll/plugin.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Plugin
     PRIORITIES = {
diff --git a/lib/jekyll/plugin_manager.rb b/lib/jekyll/plugin_manager.rb
index 979004d63b6..f53d187a337 100644
--- a/lib/jekyll/plugin_manager.rb
+++ b/lib/jekyll/plugin_manager.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class PluginManager
     attr_reader :site
diff --git a/lib/jekyll/publisher.rb b/lib/jekyll/publisher.rb
index 0b67b8c6025..26fe4a3869b 100644
--- a/lib/jekyll/publisher.rb
+++ b/lib/jekyll/publisher.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Publisher
     def initialize(site)
diff --git a/lib/jekyll/reader.rb b/lib/jekyll/reader.rb
index 903e36d3a48..5804d1f963a 100644
--- a/lib/jekyll/reader.rb
+++ b/lib/jekyll/reader.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 require "csv"
 
diff --git a/lib/jekyll/readers/collection_reader.rb b/lib/jekyll/readers/collection_reader.rb
index 062be42a4b4..7d605f421c4 100644
--- a/lib/jekyll/readers/collection_reader.rb
+++ b/lib/jekyll/readers/collection_reader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class CollectionReader
     SPECIAL_COLLECTIONS = %w(posts data).freeze
diff --git a/lib/jekyll/readers/data_reader.rb b/lib/jekyll/readers/data_reader.rb
index 63db7c6d920..e2671f2d3b4 100644
--- a/lib/jekyll/readers/data_reader.rb
+++ b/lib/jekyll/readers/data_reader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class DataReader
     attr_reader :site, :content
diff --git a/lib/jekyll/readers/layout_reader.rb b/lib/jekyll/readers/layout_reader.rb
index 985491c67a7..706dfed8c43 100644
--- a/lib/jekyll/readers/layout_reader.rb
+++ b/lib/jekyll/readers/layout_reader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class LayoutReader
     attr_reader :site
diff --git a/lib/jekyll/readers/page_reader.rb b/lib/jekyll/readers/page_reader.rb
index 507c609e507..62d7419efec 100644
--- a/lib/jekyll/readers/page_reader.rb
+++ b/lib/jekyll/readers/page_reader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class PageReader
     attr_reader :site, :dir, :unfiltered_content
diff --git a/lib/jekyll/readers/post_reader.rb b/lib/jekyll/readers/post_reader.rb
index 70688875da5..510192793b0 100644
--- a/lib/jekyll/readers/post_reader.rb
+++ b/lib/jekyll/readers/post_reader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class PostReader
     attr_reader :site, :unfiltered_content
diff --git a/lib/jekyll/readers/static_file_reader.rb b/lib/jekyll/readers/static_file_reader.rb
index 1d43d69c659..6bf07f5a0c3 100644
--- a/lib/jekyll/readers/static_file_reader.rb
+++ b/lib/jekyll/readers/static_file_reader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class StaticFileReader
     attr_reader :site, :dir, :unfiltered_content
diff --git a/lib/jekyll/readers/theme_assets_reader.rb b/lib/jekyll/readers/theme_assets_reader.rb
index 80a6547d8a7..2706690c5ce 100644
--- a/lib/jekyll/readers/theme_assets_reader.rb
+++ b/lib/jekyll/readers/theme_assets_reader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class ThemeAssetsReader
     attr_reader :site
diff --git a/lib/jekyll/regenerator.rb b/lib/jekyll/regenerator.rb
index 09ff309a28d..91ce3003bdf 100644
--- a/lib/jekyll/regenerator.rb
+++ b/lib/jekyll/regenerator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Regenerator
     attr_reader :site, :metadata, :cache
diff --git a/lib/jekyll/related_posts.rb b/lib/jekyll/related_posts.rb
index 3526a73b76f..fcccdd80eeb 100644
--- a/lib/jekyll/related_posts.rb
+++ b/lib/jekyll/related_posts.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class RelatedPosts
     class << self
diff --git a/lib/jekyll/renderer.rb b/lib/jekyll/renderer.rb
index b0f544e35e5..5a2d32a8d27 100644
--- a/lib/jekyll/renderer.rb
+++ b/lib/jekyll/renderer.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   class Renderer
diff --git a/lib/jekyll/site.rb b/lib/jekyll/site.rb
index 0bc3f1d577c..54155d0c8e2 100644
--- a/lib/jekyll/site.rb
+++ b/lib/jekyll/site.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 require "csv"
 
diff --git a/lib/jekyll/static_file.rb b/lib/jekyll/static_file.rb
index 29d71cbe8e7..55f0256c24f 100644
--- a/lib/jekyll/static_file.rb
+++ b/lib/jekyll/static_file.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class StaticFile
     attr_reader :relative_path, :extname, :name, :data
diff --git a/lib/jekyll/stevenson.rb b/lib/jekyll/stevenson.rb
index bf20b22f752..bbec66171f6 100644
--- a/lib/jekyll/stevenson.rb
+++ b/lib/jekyll/stevenson.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Stevenson < ::Logger
     def initialize
diff --git a/lib/jekyll/tags/highlight.rb b/lib/jekyll/tags/highlight.rb
index 86b9171b1fb..7ea95b0b101 100644
--- a/lib/jekyll/tags/highlight.rb
+++ b/lib/jekyll/tags/highlight.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Tags
     class HighlightBlock < Liquid::Block
diff --git a/lib/jekyll/tags/include.rb b/lib/jekyll/tags/include.rb
index 08843047a2e..ef6c8f732ca 100644
--- a/lib/jekyll/tags/include.rb
+++ b/lib/jekyll/tags/include.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 module Jekyll
   module Tags
diff --git a/lib/jekyll/tags/link.rb b/lib/jekyll/tags/link.rb
index a076c417252..77f4da9ca48 100644
--- a/lib/jekyll/tags/link.rb
+++ b/lib/jekyll/tags/link.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Tags
     class Link < Liquid::Tag
diff --git a/lib/jekyll/tags/post_url.rb b/lib/jekyll/tags/post_url.rb
index f7e52f42b57..9a1b8337c91 100644
--- a/lib/jekyll/tags/post_url.rb
+++ b/lib/jekyll/tags/post_url.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Tags
     class PostComparer
diff --git a/lib/jekyll/theme.rb b/lib/jekyll/theme.rb
index 045c91aa0c8..031c61b1e7a 100644
--- a/lib/jekyll/theme.rb
+++ b/lib/jekyll/theme.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Theme
     extend Forwardable
diff --git a/lib/jekyll/theme_builder.rb b/lib/jekyll/theme_builder.rb
index f1c97e37974..aca89dd655c 100644
--- a/lib/jekyll/theme_builder.rb
+++ b/lib/jekyll/theme_builder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Jekyll::ThemeBuilder
   SCAFFOLD_DIRECTORIES = %w(
     assets _layouts _includes _sass
diff --git a/lib/jekyll/url.rb b/lib/jekyll/url.rb
index 8f3047d30cf..f91578507da 100644
--- a/lib/jekyll/url.rb
+++ b/lib/jekyll/url.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "addressable/uri"
 
 # Public: Methods that generate a URL for a resource such as a Post or a Page.
@@ -93,7 +95,7 @@ def possible_keys(key)
 
     def generate_url_from_drop(template)
       template.gsub(%r!:([a-z_]+)!) do |match|
-        pool = possible_keys(match.sub(":".freeze, "".freeze))
+        pool = possible_keys(match.sub(":", ""))
 
         winner = pool.find { |key| @placeholders.key?(key) }
         if winner.nil?
diff --git a/lib/jekyll/utils.rb b/lib/jekyll/utils.rb
index 3f91a2b00fd..c9dcf2fd324 100644
--- a/lib/jekyll/utils.rb
+++ b/lib/jekyll/utils.rb
@@ -1,4 +1,6 @@
 
+# frozen_string_literal: true
+
 module Jekyll
   module Utils
     extend self
@@ -247,6 +249,8 @@ def slugify(string, mode: nil, cased: false)
     #
     # Returns the updated permalink template
     def add_permalink_suffix(template, permalink_style)
+      template = template.dup
+
       case permalink_style
       when :pretty
         template << "/"
@@ -256,6 +260,7 @@ def add_permalink_suffix(template, permalink_style)
         template << "/" if permalink_style.to_s.end_with?("/")
         template << ":output_ext" if permalink_style.to_s.end_with?(":output_ext")
       end
+
       template
     end
 
@@ -296,7 +301,7 @@ def safe_glob(dir, patterns, flags = 0)
     def merged_file_read_opts(site, opts)
       merged = (site ? site.file_read_opts : {}).merge(opts)
       if merged["encoding"] && !merged["encoding"].start_with?("bom|")
-        merged["encoding"].insert(0, "bom|")
+        merged["encoding"] = "bom|#{merged["encoding"]}"
       end
       merged
     end
diff --git a/lib/jekyll/utils/exec.rb b/lib/jekyll/utils/exec.rb
index 33403dbc50d..fee8b2d2e5b 100644
--- a/lib/jekyll/utils/exec.rb
+++ b/lib/jekyll/utils/exec.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "open3"
 
 module Jekyll
diff --git a/lib/jekyll/utils/platforms.rb b/lib/jekyll/utils/platforms.rb
index f66ef795bbd..f4f3382a240 100644
--- a/lib/jekyll/utils/platforms.rb
+++ b/lib/jekyll/utils/platforms.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Utils
     module Platforms
diff --git a/lib/jekyll/utils/win_tz.rb b/lib/jekyll/utils/win_tz.rb
index 06a10422274..322f5ac6230 100644
--- a/lib/jekyll/utils/win_tz.rb
+++ b/lib/jekyll/utils/win_tz.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   module Utils
     module WinTZ
diff --git a/lib/jekyll/version.rb b/lib/jekyll/version.rb
index 8a8b2b30c11..6a27620408a 100644
--- a/lib/jekyll/version.rb
+++ b/lib/jekyll/version.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   VERSION = "3.5.1".freeze
 end
diff --git a/lib/theme_template/Gemfile b/lib/theme_template/Gemfile
index 3be9c3cd812..bb94df82938 100644
--- a/lib/theme_template/Gemfile
+++ b/lib/theme_template/Gemfile
@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 source "https://rubygems.org"
 gemspec
diff --git a/rake/docs.rake b/rake/docs.rake
index fcae4f20162..e64c6cfdccd 100644
--- a/rake/docs.rake
+++ b/rake/docs.rake
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #############################################################################
 #
 # Packaging tasks for jekyll-docs
diff --git a/rake/release.rake b/rake/release.rake
index 9d9220a49a7..ce7bf41ca94 100644
--- a/rake/release.rake
+++ b/rake/release.rake
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #############################################################################
 #
 # Packaging tasks
diff --git a/rake/site.rake b/rake/site.rake
index 00ffd228b44..94aa969ea22 100644
--- a/rake/site.rake
+++ b/rake/site.rake
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #############################################################################
 #
 # Site tasks - https://jekyllrb.com
diff --git a/test/fixtures/test-dependency-theme/test-dependency-theme.gemspec b/test/fixtures/test-dependency-theme/test-dependency-theme.gemspec
index 5c260329d3b..ebc8a83c3a1 100644
--- a/test/fixtures/test-dependency-theme/test-dependency-theme.gemspec
+++ b/test/fixtures/test-dependency-theme/test-dependency-theme.gemspec
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 Gem::Specification.new do |s|
   s.name          = "test-dependency-theme"
   s.version       = "0.1.0"
diff --git a/test/fixtures/test-theme/test-theme.gemspec b/test/fixtures/test-theme/test-theme.gemspec
index 73e5deb2e94..970e1b8abdd 100644
--- a/test/fixtures/test-theme/test-theme.gemspec
+++ b/test/fixtures/test-theme/test-theme.gemspec
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 Gem::Specification.new do |s|
   s.name        = "test-theme"
   s.version     = "0.1.0"
diff --git a/test/helper.rb b/test/helper.rb
index 83beaad3c1c..3f3227bab4f 100644
--- a/test/helper.rb
+++ b/test/helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 $stdout.puts "# -------------------------------------------------------------"
 $stdout.puts "# SPECS AND TESTS ARE RUNNING WITH WARNINGS OFF."
 $stdout.puts "# SEE: https://github.com/Shopify/liquid/issues/730"
diff --git a/test/simplecov_custom_profile.rb b/test/simplecov_custom_profile.rb
index 0aaec88a58c..555acec3d7e 100644
--- a/test/simplecov_custom_profile.rb
+++ b/test/simplecov_custom_profile.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "simplecov"
 
 SimpleCov.profiles.define "gem" do
diff --git a/test/source/_plugins/dummy.rb b/test/source/_plugins/dummy.rb
index fd11d0e1044..25eef88e21b 100644
--- a/test/source/_plugins/dummy.rb
+++ b/test/source/_plugins/dummy.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Jekyll
   class Dummy < Generator
     priority :high
diff --git a/test/test_ansi.rb b/test/test_ansi.rb
index 8f18f56ec7b..9b4fd01668c 100644
--- a/test/test_ansi.rb
+++ b/test/test_ansi.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestAnsi < JekyllUnitTest
diff --git a/test/test_cleaner.rb b/test/test_cleaner.rb
index d3072e54977..65442cedc0d 100644
--- a/test/test_cleaner.rb
+++ b/test/test_cleaner.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestCleaner < JekyllUnitTest
diff --git a/test/test_coffeescript.rb b/test/test_coffeescript.rb
index 189ce05df3e..a60e0595430 100644
--- a/test/test_coffeescript.rb
+++ b/test/test_coffeescript.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestCoffeeScript < JekyllUnitTest
diff --git a/test/test_collections.rb b/test/test_collections.rb
index cb122cd9e65..e4dbe951a25 100644
--- a/test/test_collections.rb
+++ b/test/test_collections.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestCollections < JekyllUnitTest
diff --git a/test/test_command.rb b/test/test_command.rb
index 90767013b92..33e13798cc6 100644
--- a/test/test_command.rb
+++ b/test/test_command.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestCommand < JekyllUnitTest
diff --git a/test/test_commands_serve.rb b/test/test_commands_serve.rb
index ef98bab4e2b..135e83e2dba 100644
--- a/test/test_commands_serve.rb
+++ b/test/test_commands_serve.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "webrick"
 require "mercenary"
 require "helper"
diff --git a/test/test_configuration.rb b/test/test_configuration.rb
index 50156926202..dddb61b8671 100644
--- a/test/test_configuration.rb
+++ b/test/test_configuration.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 require "colorator"
 
diff --git a/test/test_convertible.rb b/test/test_convertible.rb
index ef70307062f..cc5be8785a7 100644
--- a/test/test_convertible.rb
+++ b/test/test_convertible.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 require "ostruct"
 
diff --git a/test/test_doctor_command.rb b/test/test_doctor_command.rb
index 8861440255c..182878689cc 100644
--- a/test/test_doctor_command.rb
+++ b/test/test_doctor_command.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 require "jekyll/commands/doctor"
 
diff --git a/test/test_document.rb b/test/test_document.rb
index 8726c83cd6a..42ba3c5748b 100644
--- a/test/test_document.rb
+++ b/test/test_document.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestDocument < JekyllUnitTest
diff --git a/test/test_drop.rb b/test/test_drop.rb
index 80b0d0ff693..00d2116471d 100644
--- a/test/test_drop.rb
+++ b/test/test_drop.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestDrop < JekyllUnitTest
diff --git a/test/test_entry_filter.rb b/test/test_entry_filter.rb
index 7f32653c957..c9025092318 100644
--- a/test/test_entry_filter.rb
+++ b/test/test_entry_filter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestEntryFilter < JekyllUnitTest
diff --git a/test/test_excerpt.rb b/test/test_excerpt.rb
index e0960f69663..2bcf3ba8cac 100644
--- a/test/test_excerpt.rb
+++ b/test/test_excerpt.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestExcerpt < JekyllUnitTest
diff --git a/test/test_excerpt_drop.rb b/test/test_excerpt_drop.rb
index 901b06a6f79..1eb6687266d 100644
--- a/test/test_excerpt_drop.rb
+++ b/test/test_excerpt_drop.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestExcerptDrop < JekyllUnitTest
diff --git a/test/test_filters.rb b/test/test_filters.rb
index e0eb2feee87..cb95a6449fb 100644
--- a/test/test_filters.rb
+++ b/test/test_filters.rb
@@ -1,4 +1,5 @@
 # coding: utf-8
+# frozen_string_literal: true
 
 require "helper"
 
diff --git a/test/test_front_matter_defaults.rb b/test/test_front_matter_defaults.rb
index d45ab6de9a5..9bf9629a9ed 100644
--- a/test/test_front_matter_defaults.rb
+++ b/test/test_front_matter_defaults.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestFrontMatterDefaults < JekyllUnitTest
diff --git a/test/test_generated_site.rb b/test/test_generated_site.rb
index 84345524d74..136f5fc9e68 100644
--- a/test/test_generated_site.rb
+++ b/test/test_generated_site.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestGeneratedSite < JekyllUnitTest
diff --git a/test/test_kramdown.rb b/test/test_kramdown.rb
index 6396d67201b..3861416ff2e 100644
--- a/test/test_kramdown.rb
+++ b/test/test_kramdown.rb
@@ -1,4 +1,5 @@
 # encoding: UTF-8
+# frozen_string_literal: true
 
 require "helper"
 
diff --git a/test/test_layout_reader.rb b/test/test_layout_reader.rb
index 1d32fa57892..96d2045a148 100644
--- a/test/test_layout_reader.rb
+++ b/test/test_layout_reader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestLayoutReader < JekyllUnitTest
diff --git a/test/test_liquid_extensions.rb b/test/test_liquid_extensions.rb
index a76f378623e..e281e10e5fd 100644
--- a/test/test_liquid_extensions.rb
+++ b/test/test_liquid_extensions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestLiquidExtensions < JekyllUnitTest
diff --git a/test/test_liquid_renderer.rb b/test/test_liquid_renderer.rb
index 6ba29299d67..32e980b8af9 100644
--- a/test/test_liquid_renderer.rb
+++ b/test/test_liquid_renderer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestLiquidRenderer < JekyllUnitTest
diff --git a/test/test_log_adapter.rb b/test/test_log_adapter.rb
index 7e0873ca33f..2bcd2f1d7c9 100644
--- a/test/test_log_adapter.rb
+++ b/test/test_log_adapter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestLogAdapter < JekyllUnitTest
diff --git a/test/test_new_command.rb b/test/test_new_command.rb
index 32db566d98b..c2b7def4001 100644
--- a/test/test_new_command.rb
+++ b/test/test_new_command.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 require "jekyll/commands/new"
 
diff --git a/test/test_page.rb b/test/test_page.rb
index 431c57a63ca..ed4c2c31a9a 100644
--- a/test/test_page.rb
+++ b/test/test_page.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestPage < JekyllUnitTest
diff --git a/test/test_path_sanitization.rb b/test/test_path_sanitization.rb
index 31a4b92ebff..184385fabd3 100644
--- a/test/test_path_sanitization.rb
+++ b/test/test_path_sanitization.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestPathSanitization < JekyllUnitTest
diff --git a/test/test_plugin_manager.rb b/test/test_plugin_manager.rb
index 90f057641e7..213bcef6b12 100644
--- a/test/test_plugin_manager.rb
+++ b/test/test_plugin_manager.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestPluginManager < JekyllUnitTest
diff --git a/test/test_rdiscount.rb b/test/test_rdiscount.rb
index 32289a64368..7116c29a238 100644
--- a/test/test_rdiscount.rb
+++ b/test/test_rdiscount.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestRdiscount < JekyllUnitTest
diff --git a/test/test_redcarpet.rb b/test/test_redcarpet.rb
index 4e979f4d2ee..f4208570931 100644
--- a/test/test_redcarpet.rb
+++ b/test/test_redcarpet.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestRedcarpet < JekyllUnitTest
diff --git a/test/test_regenerator.rb b/test/test_regenerator.rb
index 9e1559d4bec..3a5d35a8aa8 100644
--- a/test/test_regenerator.rb
+++ b/test/test_regenerator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestRegenerator < JekyllUnitTest
diff --git a/test/test_related_posts.rb b/test/test_related_posts.rb
index 2d6165505e3..d6a8fe6f1f3 100644
--- a/test/test_related_posts.rb
+++ b/test/test_related_posts.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestRelatedPosts < JekyllUnitTest
diff --git a/test/test_sass.rb b/test/test_sass.rb
index 3a9df0aeae3..15b04162f01 100644
--- a/test/test_sass.rb
+++ b/test/test_sass.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestSass < JekyllUnitTest
diff --git a/test/test_site.rb b/test/test_site.rb
index d039cb8a924..adc69e33436 100644
--- a/test/test_site.rb
+++ b/test/test_site.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestSite < JekyllUnitTest
diff --git a/test/test_site_drop.rb b/test/test_site_drop.rb
index b836c70d3eb..43c52d708a5 100644
--- a/test/test_site_drop.rb
+++ b/test/test_site_drop.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestSiteDrop < JekyllUnitTest
diff --git a/test/test_static_file.rb b/test/test_static_file.rb
index 49adc96b79f..edfc9facf0e 100644
--- a/test/test_static_file.rb
+++ b/test/test_static_file.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestStaticFile < JekyllUnitTest
diff --git a/test/test_tags.rb b/test/test_tags.rb
index 68fd40398a8..7a60ec9dc18 100644
--- a/test/test_tags.rb
+++ b/test/test_tags.rb
@@ -1,4 +1,5 @@
 # coding: utf-8
+# frozen_string_literal: true
 
 require "helper"
 
diff --git a/test/test_theme.rb b/test/test_theme.rb
index 3d557dc8ca0..69628dde1ba 100644
--- a/test/test_theme.rb
+++ b/test/test_theme.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestTheme < JekyllUnitTest
diff --git a/test/test_theme_assets_reader.rb b/test/test_theme_assets_reader.rb
index 8d792f735d9..358789f529a 100644
--- a/test/test_theme_assets_reader.rb
+++ b/test/test_theme_assets_reader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestThemeAssetsReader < JekyllUnitTest
diff --git a/test/test_url.rb b/test/test_url.rb
index 23ab9735861..859babd4574 100644
--- a/test/test_url.rb
+++ b/test/test_url.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestURL < JekyllUnitTest
diff --git a/test/test_utils.rb b/test/test_utils.rb
index 5f5611ce55e..1b4d4813b66 100644
--- a/test/test_utils.rb
+++ b/test/test_utils.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "helper"
 
 class TestUtils < JekyllUnitTest