diff --git a/app/logical/visible_string_validator.rb b/app/logical/visible_string_validator.rb
new file mode 100644
index 000000000..0716f588b
--- /dev/null
+++ b/app/logical/visible_string_validator.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+# A custom validator for ensuring a string isn't blank. Like the `presence` validator, but checks for certain invisible
+# Unicode characters such as zero-width spaces too.
+#
+# @example
+#   validates :body, visible_string: true
+#
+# @see https://invisible-characters.com/
+# @see https://guides.rubyonrails.org/active_record_validations.html#presence
+# @see https://guides.rubyonrails.org/active_record_validations.html#custom-validators
+class VisibleStringValidator < ActiveModel::EachValidator
+  def validate_each(record, attr, string)
+    return if options[:allow_empty] && string.empty?
+
+    if string.nil? || string.invisible?
+      record.errors.add(attr, "can't be blank")
+    end
+  end
+end
diff --git a/app/models/ban.rb b/app/models/ban.rb
index bc5747476..16c3fd61c 100644
--- a/app/models/ban.rb
+++ b/app/models/ban.rb
@@ -14,7 +14,7 @@ class Ban < ApplicationRecord
 
   validates :duration, presence: true
   validates :duration, inclusion: { in: [1.day, 3.days, 1.week, 1.month, 3.months, 6.months, 1.year, 100.years], message: "%{value} is not a valid ban duration" }, if: :duration_changed?
-  validates :reason, presence: true
+  validates :reason, visible_string: true
   validate :user, :validate_user_is_bannable, on: :create
 
   scope :unexpired, -> { where("bans.created_at + bans.duration > ?", Time.zone.now) }
diff --git a/app/models/bulk_update_request.rb b/app/models/bulk_update_request.rb
index 61d6cca9d..91f740531 100644
--- a/app/models/bulk_update_request.rb
+++ b/app/models/bulk_update_request.rb
@@ -10,9 +10,9 @@ class BulkUpdateRequest < ApplicationRecord
   belongs_to :forum_post, optional: true
   belongs_to :approver, optional: true, class_name: "User"
 
-  validates :reason, presence: true, on: :create
-  validates :script, presence: true
-  validates :title, presence: true, if: ->(rec) { rec.forum_topic_id.blank? }
+  validates :reason, visible_string: true, on: :create
+  validates :script, visible_string: true
+  validates :title, visible_string: true, if: ->(rec) { rec.forum_topic_id.blank? }
   validates :forum_topic, presence: true, if: ->(rec) { rec.forum_topic_id.present? }
   validates :status, inclusion: { in: STATUSES }
   validate :validate_script, if: :script_changed?
diff --git a/app/models/comment.rb b/app/models/comment.rb
index 4eeb6d16e..19fdbaa58 100644
--- a/app/models/comment.rb
+++ b/app/models/comment.rb
@@ -13,7 +13,7 @@ class Comment < ApplicationRecord
   has_many :active_votes, -> { active }, class_name: "CommentVote"
   has_many :mod_actions, as: :subject, dependent: :destroy
 
-  validates :body, presence: true, length: { maximum: 15_000 }, if: :body_changed?
+  validates :body, visible_string: true, length: { maximum: 15_000 }, if: :body_changed?
 
   before_create :autoreport_spam
   before_save :handle_reports_on_deletion
diff --git a/app/models/dmail.rb b/app/models/dmail.rb
index 1b6cbf788..2bfde03a7 100644
--- a/app/models/dmail.rb
+++ b/app/models/dmail.rb
@@ -4,8 +4,8 @@ class Dmail < ApplicationRecord
   attr_accessor :creator_ip_addr, :disable_email_notifications
 
   validate :validate_sender_is_not_limited, on: :create
-  validates :title, presence: true, length: { maximum: 200 }, if: :title_changed?
-  validates :body, presence: true, length: { maximum: 50_000 }, if: :body_changed?
+  validates :title, visible_string: true, length: { maximum: 200 }, if: :title_changed?
+  validates :body, visible_string: true, length: { maximum: 50_000 }, if: :body_changed?
 
   belongs_to :owner, :class_name => "User"
   belongs_to :to, :class_name => "User"
diff --git a/app/models/favorite_group.rb b/app/models/favorite_group.rb
index 9d744b102..4e80c5fbe 100644
--- a/app/models/favorite_group.rb
+++ b/app/models/favorite_group.rb
@@ -5,7 +5,7 @@ class FavoriteGroup < ApplicationRecord
 
   before_validation :normalize_name
 
-  validates :name, presence: true
+  validates :name, visible_string: true
   validates :name, uniqueness: { case_sensitive: false, scope: :creator_id }
   validate :validate_name, if: :name_changed?
   validate :creator_can_create_favorite_groups, :on => :create
diff --git a/app/models/forum_post.rb b/app/models/forum_post.rb
index cb5e6ec72..fbc4652f2 100644
--- a/app/models/forum_post.rb
+++ b/app/models/forum_post.rb
@@ -16,7 +16,7 @@ class ForumPost < ApplicationRecord
   has_one :tag_implication
   has_one :bulk_update_request
 
-  validates :body, presence: true, length: { maximum: 200_000 }, if: :body_changed?
+  validates :body, visible_string: true, length: { maximum: 200_000 }, if: :body_changed?
   validate :validate_deletion_of_original_post
   validate :validate_undeletion_of_post
 
diff --git a/app/models/forum_topic.rb b/app/models/forum_topic.rb
index fd8af88b2..a53d4e054 100644
--- a/app/models/forum_topic.rb
+++ b/app/models/forum_topic.rb
@@ -27,7 +27,7 @@ class ForumTopic < ApplicationRecord
   has_many :tag_implications
   has_many :mod_actions, as: :subject, dependent: :destroy
 
-  validates :title, presence: true, length: { maximum: 200 }, if: :title_changed?
+  validates :title, visible_string: true, length: { maximum: 200 }, if: :title_changed?
   validates :category_id, inclusion: { in: CATEGORIES.keys }
   validates :min_level, inclusion: { in: MIN_LEVELS.values }
 
diff --git a/app/models/ip_ban.rb b/app/models/ip_ban.rb
index 8440ea345..60fc911c1 100644
--- a/app/models/ip_ban.rb
+++ b/app/models/ip_ban.rb
@@ -7,7 +7,7 @@ class IpBan < ApplicationRecord
   has_many :mod_actions, as: :subject, dependent: :destroy
 
   validate :validate_ip_addr
-  validates :reason, presence: true
+  validates :reason, visible_string: true
 
   after_save :create_mod_action
 
diff --git a/app/models/moderation_report.rb b/app/models/moderation_report.rb
index 60e4d4f92..d6e192202 100644
--- a/app/models/moderation_report.rb
+++ b/app/models/moderation_report.rb
@@ -10,7 +10,7 @@ class ModerationReport < ApplicationRecord
   has_many :mod_actions, as: :subject, dependent: :destroy
 
   before_validation(on: :create) { model.lock! }
-  validates :reason, presence: true
+  validates :reason, visible_string: true
   validates :model_type, inclusion: { in: MODEL_TYPES }
   validates :creator, uniqueness: { scope: [:model_type, :model_id], message: "have already reported this message." }, on: :create
 
diff --git a/app/models/note.rb b/app/models/note.rb
index 3bde8579f..bd0625f85 100644
--- a/app/models/note.rb
+++ b/app/models/note.rb
@@ -11,7 +11,7 @@ class Note < ApplicationRecord
   validates :y, presence: true
   validates :width, presence: true
   validates :height, presence: true
-  validates :body, presence: true
+  validates :body, visible_string: true
   validate :note_within_image
   after_save :update_post
   after_save :create_version
diff --git a/app/models/pool.rb b/app/models/pool.rb
index 0a66afd2d..6250c08e7 100644
--- a/app/models/pool.rb
+++ b/app/models/pool.rb
@@ -6,7 +6,7 @@ class Pool < ApplicationRecord
 
   array_attribute :post_ids, parse: /\d+/, cast: :to_i
 
-  validates :name, uniqueness: { case_sensitive: false }, if: :name_changed?
+  validates :name, visible_string: true, uniqueness: { case_sensitive: false }, if: :name_changed?
   validate :validate_name, if: :name_changed?
   validates :category, inclusion: { in: %w[series collection] }
   validate :updater_can_edit_deleted
diff --git a/app/models/post_appeal.rb b/app/models/post_appeal.rb
index de0c5612d..437781f88 100644
--- a/app/models/post_appeal.rb
+++ b/app/models/post_appeal.rb
@@ -4,7 +4,7 @@ class PostAppeal < ApplicationRecord
   belongs_to :creator, :class_name => "User"
   belongs_to :post
 
-  validates :reason, length: { maximum: 140 }
+  validates :reason, visible_string: { allow_empty: true }, length: { maximum: 140 }
   validate :validate_post_is_appealable, on: :create
   validate :validate_creator_is_not_limited, on: :create
   validates :creator, uniqueness: { scope: :post, message: "have already appealed this post" }, on: :create
diff --git a/app/models/post_flag.rb b/app/models/post_flag.rb
index 10ad3bc2c..011a6687f 100644
--- a/app/models/post_flag.rb
+++ b/app/models/post_flag.rb
@@ -10,7 +10,7 @@ class PostFlag < ApplicationRecord
   belongs_to :post
 
   before_validation { post.lock! }
-  validates :reason, presence: true, length: { in: 1..140 }
+  validates :reason, visible_string: true, length: { in: 1..140 }
   validate :validate_creator_is_not_limited, on: :create
   validate :validate_post, on: :create
   validates :creator_id, uniqueness: { scope: :post_id, on: :create, unless: :is_deletion, message: "have already flagged this post" }
diff --git a/app/models/saved_search.rb b/app/models/saved_search.rb
index c4d547f64..da50b3ce9 100644
--- a/app/models/saved_search.rb
+++ b/app/models/saved_search.rb
@@ -11,7 +11,7 @@ class SavedSearch < ApplicationRecord
   normalize :query, :normalize_query
   normalize :labels, :normalize_labels
 
-  validates :query, presence: true
+  validates :query, visible_string: true
   validate :validate_count, on: :create
 
   scope :labeled, ->(label) { where_array_includes_any_lower(:labels, [normalize_label(label)]) }
diff --git a/app/models/user_feedback.rb b/app/models/user_feedback.rb
index 17c3611e6..3930d08ce 100644
--- a/app/models/user_feedback.rb
+++ b/app/models/user_feedback.rb
@@ -7,7 +7,7 @@ class UserFeedback < ApplicationRecord
 
   belongs_to :user
   belongs_to :creator, class_name: "User"
-  validates :body, presence: true
+  validates :body, visible_string: true
   validates :category, presence: true, inclusion: { in: %w[positive negative neutral] }
   after_create :create_dmail, unless: :disable_dmail_notification
   after_update :create_mod_action
diff --git a/app/models/wiki_page.rb b/app/models/wiki_page.rb
index 240824ccc..d6a92a510 100644
--- a/app/models/wiki_page.rb
+++ b/app/models/wiki_page.rb
@@ -14,7 +14,7 @@ class WikiPage < ApplicationRecord
   array_attribute :other_names # XXX must come after `normalize :other_names`
 
   validates :title, tag_name: true, presence: true, uniqueness: true, if: :title_changed?
-  validates :body, presence: true, unless: -> { is_deleted? || other_names.present? }
+  validates :body, visible_string: true, unless: -> { is_deleted? || other_names.present? }
   validate :validate_rename
   validate :validate_other_names
 
diff --git a/config/initializers/core_extensions.rb b/config/initializers/core_extensions.rb
index 1dbf8c990..19272c542 100644
--- a/config/initializers/core_extensions.rb
+++ b/config/initializers/core_extensions.rb
@@ -5,6 +5,22 @@ require "danbooru"
 module Danbooru
   module Extensions
     module String
+      # https://invisible-characters.com
+      # https://character.construction/blanks
+      # https://www.unicode.org/review/pr-5.html (5.22 Default Ignorable Code Points)
+      # https://en.wikipedia.org/wiki/Whitespace_character
+      #
+      # [[:space:]] = https://codepoints.net/search?gc[]=Z (Space_Separator | Line_Separator | Paragraph_Separator | U+0009 | U+000A | U+000B | U+000C | U+000D | U+0085)
+      # \p{di} = https://codepoints.net/search?DI=1 (Default_Ignorable_Code_Point)
+      # \u2800 = https://codepoints.net/U+2800 (BRAILLE PATTERN BLANK)
+      INVISIBLE_REGEX = /\A[[:space:]\p{di}\u2800]*\z/
+
+      # Returns true if the string consists entirely of invisible characters. Like `#blank?`, but includes control
+      # characters and certain other invisible Unicode characters that aren't classified as spaces.
+      def invisible?
+        match?(INVISIBLE_REGEX)
+      end
+
       def to_escaped_for_sql_like
         string = self.gsub(/%|_|\*|\\\*|\\\\|\\/) do |str|
           case str
diff --git a/test/unit/comment_test.rb b/test/unit/comment_test.rb
index 5eb39ad2b..8c2b63c4d 100644
--- a/test/unit/comment_test.rb
+++ b/test/unit/comment_test.rb
@@ -202,8 +202,11 @@ class CommentTest < ActiveSupport::TestCase
     end
 
     context "during validation" do
-      subject { FactoryBot.build(:comment) }
+      subject { build(:comment) }
+
+      should_not allow_value("").for(:body)
       should_not allow_value(" ").for(:body)
+      should_not allow_value("\u200B").for(:body)
     end
   end
 end
diff --git a/test/unit/dmail_test.rb b/test/unit/dmail_test.rb
index 5f25bff0f..6269021df 100644
--- a/test/unit/dmail_test.rb
+++ b/test/unit/dmail_test.rb
@@ -149,8 +149,12 @@ class DmailTest < ActiveSupport::TestCase
     context "during validation" do
       subject { FactoryBot.build(:dmail) }
 
+      should_not allow_value("").for(:title)
       should_not allow_value(" ").for(:title)
+      should_not allow_value("\u200B").for(:title)
+      should_not allow_value("").for(:body)
       should_not allow_value(" ").for(:body)
+      should_not allow_value("\u200B").for(:body)
       should_not allow_value(nil).for(:to)
       should_not allow_value(nil).for(:from)
       should_not allow_value(nil).for(:owner)
diff --git a/test/unit/favorite_group_test.rb b/test/unit/favorite_group_test.rb
index a5f9e8d89..26699157f 100644
--- a/test/unit/favorite_group_test.rb
+++ b/test/unit/favorite_group_test.rb
@@ -68,5 +68,8 @@ class FavoriteGroupTest < ActiveSupport::TestCase
     should_not allow_value("_").for(:name)
     should_not allow_value("any").for(:name)
     should_not allow_value("none").for(:name)
+    should_not allow_value("").for(:name)
+    should_not allow_value("   ").for(:name)
+    should_not allow_value("\u200B").for(:name)
   end
 end
diff --git a/test/unit/forum_post_test.rb b/test/unit/forum_post_test.rb
index b29b646a4..e082d0441 100644
--- a/test/unit/forum_post_test.rb
+++ b/test/unit/forum_post_test.rb
@@ -165,5 +165,13 @@ class ForumPostTest < ActiveSupport::TestCase
         assert_equal(@second_user.id, @post.updater_id)
       end
     end
+
+    context "during validation" do
+      subject { build(:forum_post) }
+
+      should_not allow_value("").for(:body)
+      should_not allow_value(" ").for(:body)
+      should_not allow_value("\u200B").for(:body)
+    end
   end
 end
diff --git a/test/unit/forum_topic_test.rb b/test/unit/forum_topic_test.rb
index 207fa4f75..3d3bd0597 100644
--- a/test/unit/forum_topic_test.rb
+++ b/test/unit/forum_topic_test.rb
@@ -82,5 +82,13 @@ class ForumTopicTest < ActiveSupport::TestCase
         end
       end
     end
+
+    context "during validation" do
+      subject { build(:forum_topic) }
+
+      should_not allow_value("").for(:title)
+      should_not allow_value(" ").for(:title)
+      should_not allow_value("\u200B").for(:title)
+    end
   end
 end
diff --git a/test/unit/note_test.rb b/test/unit/note_test.rb
index 6129156f1..194a5a79c 100644
--- a/test/unit/note_test.rb
+++ b/test/unit/note_test.rb
@@ -145,5 +145,11 @@ class NoteTest < ActiveSupport::TestCase
         end
       end
     end
+
+    context "when validating notes" do
+      should_not allow_value("").for(:body)
+      should_not allow_value("   ").for(:body)
+      should_not allow_value("\u200B").for(:body)
+    end
   end
 end
diff --git a/test/unit/pool_test.rb b/test/unit/pool_test.rb
index 8e2ba5f32..bd5d29cc8 100644
--- a/test/unit/pool_test.rb
+++ b/test/unit/pool_test.rb
@@ -244,9 +244,17 @@ class PoolTest < ActiveSupport::TestCase
     end
 
     context "when validating names" do
-      ["foo,bar", "foo*bar", "123", "___", "   ", "any", "none", "series", "collection"].each do |bad_name|
-        should_not allow_value(bad_name).for(:name)
-      end
+      should_not allow_value("foo,bar").for(:name)
+      should_not allow_value("foo*bar").for(:name)
+      should_not allow_value("123").for(:name)
+      should_not allow_value("any").for(:name)
+      should_not allow_value("none").for(:name)
+      should_not allow_value("series").for(:name)
+      should_not allow_value("collection").for(:name)
+      should_not allow_value("___").for(:name)
+      should_not allow_value("   ").for(:name)
+      should_not allow_value("\u200B").for(:name)
+      should_not allow_value("").for(:name)
     end
   end
 
diff --git a/test/unit/post_appeal_test.rb b/test/unit/post_appeal_test.rb
index e69f97ab8..1b52d3d36 100644
--- a/test/unit/post_appeal_test.rb
+++ b/test/unit/post_appeal_test.rb
@@ -52,6 +52,15 @@ class PostAppealTest < ActiveSupport::TestCase
           end
         end
       end
+
+      context "validation" do
+        subject { build(:post_appeal) }
+
+        should allow_value("").for(:reason)
+
+        should_not allow_value(" ").for(:reason)
+        should_not allow_value("\u200B").for(:reason)
+      end
     end
   end
 end
diff --git a/test/unit/post_flag_test.rb b/test/unit/post_flag_test.rb
index dde365a72..98db81a6d 100644
--- a/test/unit/post_flag_test.rb
+++ b/test/unit/post_flag_test.rb
@@ -114,5 +114,13 @@ class PostFlagTest < ActiveSupport::TestCase
         end
       end
     end
+
+    context "during validation" do
+      subject { build(:post_flag) }
+
+      should_not allow_value("").for(:reason)
+      should_not allow_value(" ").for(:reason)
+      should_not allow_value("\u200B").for(:reason)
+    end
   end
 end
diff --git a/test/unit/string_test.rb b/test/unit/string_test.rb
index 1691d4ec2..c178c8633 100644
--- a/test/unit/string_test.rb
+++ b/test/unit/string_test.rb
@@ -41,4 +41,26 @@ class StringTest < ActiveSupport::TestCase
       assert_equal("foo\r\nbar", "foo\u2029bar".normalize_whitespace)
     end
   end
+
+  context "String#invisible?" do
+    should "work" do
+      assert_equal(true, "".invisible?)
+      assert_equal(true, " ".invisible?)
+      assert_equal(true, "\v\t\f\r\n".invisible?)
+      assert_equal(true, "\u00A0\u00AD\u034F\u061C\u115F\u1160\u17B4\u17B5\u180B\u180C\u180D\u180E".invisible?)
+      assert_equal(true, "\u200B\u200C\u200D\u200E\u200F\u2028\u2029\u2060\u206F\u2800\u3000\u3164".invisible?)
+      assert_equal(true, "\uFE00\uFE0F\uFEFF\uFFA0".invisible?)
+      assert_equal(true, "\u{E0001}\u{E007F}".invisible?)
+
+      assert_equal(false, "foo".invisible?)
+      assert_equal(false, "\u0000".invisible?) # https://codepoints.net/U+0000 (NULL)
+      assert_equal(false, "\u0001".invisible?) # https://codepoints.net/U+0001 (START OF HEADING)
+      assert_equal(false, "\uE000".invisible?) # https://codepoints.net/U+E000 (PRIVATE USE CHARACTER)
+      assert_equal(false, "\uFDD0".invisible?) # https://codepoints.net/U+FDD0 (NONCHARACTER)
+      assert_equal(false, "\uFFF9".invisible?) # https://codepoints.net/U+FFF9 (INTERLINEAR ANNOTATION ANCHOR)
+      assert_equal(false, "\uFFFF".invisible?) # https://codepoints.net/U+FFFF (NONCHARACTER)
+      assert_equal(false, "\u{1D159}".invisible?) # https://codepoints.net/U+1D159 (MUSICAL SYMBOL NULL NOTEHEAD)
+      assert_equal(false, "\u{1D455}".invisible?) # https://codepoints.net/U+1D455 (<reserved>)
+    end
+  end
 end
diff --git a/test/unit/user_feedback_test.rb b/test/unit/user_feedback_test.rb
index 5f20faa66..034af6e7c 100644
--- a/test/unit/user_feedback_test.rb
+++ b/test/unit/user_feedback_test.rb
@@ -17,5 +17,11 @@ class UserFeedbackTest < ActiveSupport::TestCase
         assert_equal(dmail, user.dmails.last.body)
       end
     end
+
+    context "on validation" do
+      should_not allow_value("").for(:body)
+      should_not allow_value("   ").for(:body)
+      should_not allow_value("\u200B").for(:body)
+    end
   end
 end
diff --git a/test/unit/wiki_page_test.rb b/test/unit/wiki_page_test.rb
index 4a754b886..ce2c3a8d4 100644
--- a/test/unit/wiki_page_test.rb
+++ b/test/unit/wiki_page_test.rb
@@ -114,6 +114,8 @@ class WikiPageTest < ActiveSupport::TestCase
       should normalize_attribute(:title).from(" Foo___   Bar ").to("foo_bar")
 
       should_not allow_value("").for(:title).on(:create)
+      should_not allow_value(" ").for(:title).on(:create)
+      should_not allow_value("\u200B").for(:title).on(:create)
       should_not allow_value("___").for(:title).on(:create)
       should_not allow_value("-foo").for(:title).on(:create)
       should_not allow_value("/foo").for(:title).on(:create)
@@ -126,6 +128,12 @@ class WikiPageTest < ActiveSupport::TestCase
       should_not allow_value("X"*171).for(:title).on(:create)
     end
 
+    context "during body validation" do
+      should_not allow_value("").for(:body)
+      should_not allow_value(" ").for(:body)
+      should_not allow_value("\u200B").for(:body)
+    end
+
     context "with other names" do
       should "not allow artist wikis to have other names" do
         tag = create(:artist_tag)