diff --git a/lib/docs/filters/core/attribution.rb b/lib/docs/filters/core/attribution.rb
index e5923d51..1bed0eba 100644
--- a/lib/docs/filters/core/attribution.rb
+++ b/lib/docs/filters/core/attribution.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Docs
   class AttributionFilter < Filter
     def call
diff --git a/lib/docs/filters/core/clean_html.rb b/lib/docs/filters/core/clean_html.rb
index ddb26013..f17333c0 100644
--- a/lib/docs/filters/core/clean_html.rb
+++ b/lib/docs/filters/core/clean_html.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Docs
   class CleanHtmlFilter < Filter
     def call
diff --git a/lib/docs/filters/core/clean_local_urls.rb b/lib/docs/filters/core/clean_local_urls.rb
index 15954a6b..83e9a6a0 100644
--- a/lib/docs/filters/core/clean_local_urls.rb
+++ b/lib/docs/filters/core/clean_local_urls.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Docs
   class CleanLocalUrlsFilter < Filter
     def call
diff --git a/lib/docs/filters/core/clean_text.rb b/lib/docs/filters/core/clean_text.rb
index 1b823c59..d49e1448 100644
--- a/lib/docs/filters/core/clean_text.rb
+++ b/lib/docs/filters/core/clean_text.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Docs
   class CleanTextFilter < Filter
     EMPTY_NODES_RGX = /<(?!td|th|iframe|mspace)(\w+)[^>]*>[[:space:]]*<\/\1>/
diff --git a/lib/docs/filters/core/container.rb b/lib/docs/filters/core/container.rb
index c3e89843..ad700b73 100644
--- a/lib/docs/filters/core/container.rb
+++ b/lib/docs/filters/core/container.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Docs
   class ContainerFilter < Filter
     class ContainerNotFound < StandardError; end
diff --git a/lib/docs/filters/core/entries.rb b/lib/docs/filters/core/entries.rb
index 30f7c4e9..43af4095 100644
--- a/lib/docs/filters/core/entries.rb
+++ b/lib/docs/filters/core/entries.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Docs
   class EntriesFilter < Filter
     def call
diff --git a/lib/docs/filters/core/inner_html.rb b/lib/docs/filters/core/inner_html.rb
index bc89c99e..99302eda 100644
--- a/lib/docs/filters/core/inner_html.rb
+++ b/lib/docs/filters/core/inner_html.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Docs
   class InnerHtmlFilter < Filter
     def call
diff --git a/lib/docs/filters/core/internal_urls.rb b/lib/docs/filters/core/internal_urls.rb
index eb7724c3..e5770eef 100644
--- a/lib/docs/filters/core/internal_urls.rb
+++ b/lib/docs/filters/core/internal_urls.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Docs
   class InternalUrlsFilter < Filter
     def call
diff --git a/lib/docs/filters/core/normalize_paths.rb b/lib/docs/filters/core/normalize_paths.rb
index dde9b9df..35a0f48d 100644
--- a/lib/docs/filters/core/normalize_paths.rb
+++ b/lib/docs/filters/core/normalize_paths.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Docs
   class NormalizePathsFilter < Filter
     def call
diff --git a/lib/docs/filters/core/normalize_urls.rb b/lib/docs/filters/core/normalize_urls.rb
index 98d8215d..3d0dc7bb 100644
--- a/lib/docs/filters/core/normalize_urls.rb
+++ b/lib/docs/filters/core/normalize_urls.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Docs
   class NormalizeUrlsFilter < Filter
     ATTRIBUTES = { a: 'href', img: 'src', iframe: 'src' }
diff --git a/lib/docs/filters/core/title.rb b/lib/docs/filters/core/title.rb
index 76860af8..1d4eb88a 100644
--- a/lib/docs/filters/core/title.rb
+++ b/lib/docs/filters/core/title.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Docs
   class TitleFilter < Filter
     def call