diff --git a/app/helpers/posts_helper.rb b/app/helpers/posts_helper.rb
index f1ea2f60a..12cd1a2eb 100644
--- a/app/helpers/posts_helper.rb
+++ b/app/helpers/posts_helper.rb
@@ -25,7 +25,7 @@ module PostsHelper
     return unless post_search_counts_enabled?
     return unless params[:action] == "index" && params[:page].nil? && params[:tags].present?
 
-    tags = Tag.scan_query(params[:tags]).sort.join(" ")
+    tags = PostQueryBuilder.scan_query(params[:tags]).sort.join(" ")
     sig = generate_reportbooru_signature("ps-#{tags}")
     render "posts/partials/index/search_count", sig: sig
   end
@@ -63,7 +63,7 @@ module PostsHelper
   end
 
   def show_tag_change_notice?
-    Tag.scan_query(params[:tags]).size == 1 && TagChangeNoticeService.get_forum_topic_id(params[:tags])
+    PostQueryBuilder.scan_query(params[:tags]).size == 1 && TagChangeNoticeService.get_forum_topic_id(params[:tags])
   end
 
   private
diff --git a/app/javascript/src/javascripts/autocomplete.js.erb b/app/javascript/src/javascripts/autocomplete.js.erb
index 9e052579b..c207da5fc 100644
--- a/app/javascript/src/javascripts/autocomplete.js.erb
+++ b/app/javascript/src/javascripts/autocomplete.js.erb
@@ -3,9 +3,9 @@ import CurrentUser from './current_user'
 let Autocomplete = {};
 
 /* eslint-disable */
-Autocomplete.METATAGS = <%= Tag::METATAGS.to_json.html_safe %>;
+Autocomplete.METATAGS = <%= PostQueryBuilder::METATAGS.to_json.html_safe %>;
 Autocomplete.TAG_CATEGORIES = <%= TagCategory.mapping.to_json.html_safe %>;
-Autocomplete.ORDER_METATAGS = <%= Tag::ORDER_METATAGS.to_json.html_safe %>;
+Autocomplete.ORDER_METATAGS = <%= PostQueryBuilder::ORDER_METATAGS.to_json.html_safe %>;
 /* eslint-enable */
 
 Autocomplete.TAG_PREFIXES = "-|~|" + Object.keys(Autocomplete.TAG_CATEGORIES).map(category => category + ":").join("|");
diff --git a/app/jobs/tag_batch_change_job.rb b/app/jobs/tag_batch_change_job.rb
index 542752d13..17ec1b4c9 100644
--- a/app/jobs/tag_batch_change_job.rb
+++ b/app/jobs/tag_batch_change_job.rb
@@ -6,8 +6,8 @@ class TagBatchChangeJob < ApplicationJob
   def perform(antecedent, consequent, updater, updater_ip_addr)
     raise Error.new("antecedent is missing") if antecedent.blank?
 
-    normalized_antecedent = TagAlias.to_aliased(::Tag.scan_tags(antecedent.mb_chars.downcase))
-    normalized_consequent = TagAlias.to_aliased(::Tag.scan_tags(consequent.mb_chars.downcase))
+    normalized_antecedent = TagAlias.to_aliased(PostQueryBuilder.scan_query(antecedent.mb_chars.downcase))
+    normalized_consequent = TagAlias.to_aliased(PostQueryBuilder.scan_query(consequent.mb_chars.downcase))
 
     CurrentUser.without_safe_mode do
       CurrentUser.scoped(updater, updater_ip_addr) do
@@ -30,7 +30,7 @@ class TagBatchChangeJob < ApplicationJob
   end
 
   def migrate_saved_searches(normalized_antecedent, normalized_consequent)
-    tags = Tag.scan_tags(normalized_antecedent.join(" "), strip_metatags: true)
+    tags = PostQueryBuilder.scan_query(normalized_antecedent.join(" "), strip_metatags: true)
 
     # https://www.postgresql.org/docs/current/static/functions-array.html
     saved_searches = SavedSearch.where("string_to_array(query, ' ') @> ARRAY[?]", tags)
@@ -53,7 +53,7 @@ class TagBatchChangeJob < ApplicationJob
 
       begin
         repl = user.blacklisted_tags.split(/\r\n|\r|\n/).map do |line|
-          list = Tag.scan_tags(line)
+          list = PostQueryBuilder.scan_query(line)
 
           if (list & query).size != query.size
             next line
diff --git a/app/logical/alias_and_implication_importer.rb b/app/logical/alias_and_implication_importer.rb
index ccf5502e0..c55979399 100644
--- a/app/logical/alias_and_implication_importer.rb
+++ b/app/logical/alias_and_implication_importer.rb
@@ -88,8 +88,8 @@ class AliasAndImplicationImporter
         all
 
       when :mass_update
-        all += Tag.scan_tags(token[1])
-        all += Tag.scan_tags(token[2])
+        all += PostQueryBuilder.scan_query(token[1])
+        all += PostQueryBuilder.scan_query(token[2])
         all
 
       when :change_category
diff --git a/app/logical/concerns/searchable.rb b/app/logical/concerns/searchable.rb
index ea40005ae..ce5265ecc 100644
--- a/app/logical/concerns/searchable.rb
+++ b/app/logical/concerns/searchable.rb
@@ -64,7 +64,7 @@ module Searchable
   def where_array_count(attr, value)
     relation = all
     qualified_column = "cardinality(#{qualified_column_for(attr)})"
-    parsed_range = Tag.parse_helper(value, :integer)
+    parsed_range = PostQueryBuilder.parse_helper(value, :integer)
 
     PostQueryBuilder.new(nil).add_range_relation(parsed_range, qualified_column, relation)
   end
@@ -96,7 +96,7 @@ module Searchable
 
     column = column_for_attribute(attribute)
     qualified_column = "#{table_name}.#{column.name}"
-    parsed_range = Tag.parse_helper(range, column.type)
+    parsed_range = PostQueryBuilder.parse_helper(range, column.type)
 
     PostQueryBuilder.new(nil).add_range_relation(parsed_range, qualified_column, self)
   end
@@ -252,7 +252,7 @@ module Searchable
 
   def apply_default_order(params)
     if params[:order] == "custom"
-      parse_ids = Tag.parse_helper(params[:id])
+      parse_ids = PostQueryBuilder.parse_helper(params[:id])
       if parse_ids[0] == :in
         return find_ordered(parse_ids[1])
       end
diff --git a/app/logical/post_query_builder.rb b/app/logical/post_query_builder.rb
index be3a5f839..663a71153 100644
--- a/app/logical/post_query_builder.rb
+++ b/app/logical/post_query_builder.rb
@@ -1,4 +1,49 @@
 class PostQueryBuilder
+  COUNT_METATAGS = %w[
+    comment_count deleted_comment_count active_comment_count
+    note_count deleted_note_count active_note_count
+    flag_count resolved_flag_count unresolved_flag_count
+    child_count deleted_child_count active_child_count
+    pool_count deleted_pool_count active_pool_count series_pool_count collection_pool_count
+    appeal_count approval_count replacement_count
+  ]
+
+  # allow e.g. `deleted_comments` as a synonym for `deleted_comment_count`
+  COUNT_METATAG_SYNONYMS = COUNT_METATAGS.map { |str| str.delete_suffix("_count").pluralize }
+
+  METATAGS = %w[
+    -user user -approver approver commenter comm noter noteupdater artcomm
+    -pool pool ordpool -favgroup favgroup -fav fav ordfav md5 -rating rating
+    -locked locked width height mpixels ratio score favcount filesize source
+    -source id -id date age order limit -status status tagcount parent -parent
+    child pixiv_id pixiv search upvote downvote filetype -filetype flagger
+    -flagger appealer -appealer disapproved -disapproved embedded
+  ] + TagCategory.short_name_list.map {|x| "#{x}tags"} + COUNT_METATAGS + COUNT_METATAG_SYNONYMS
+
+  ORDER_METATAGS = %w[
+    id id_desc
+    score score_asc
+    favcount favcount_asc
+    created_at created_at_asc
+    change change_asc
+    comment comment_asc
+    comment_bumped comment_bumped_asc
+    note note_asc
+    artcomm artcomm_asc
+    mpixels mpixels_asc
+    portrait landscape
+    filesize filesize_asc
+    tagcount tagcount_asc
+    rank
+    curated
+    modqueue
+    random
+    custom
+  ] +
+    COUNT_METATAGS +
+    COUNT_METATAG_SYNONYMS.flat_map { |str| [str, "#{str}_asc"] } +
+    TagCategory.short_name_list.flat_map { |str| ["#{str}tags", "#{str}tags_asc"] }
+
   attr_accessor :query_string
 
   def initialize(query_string)
@@ -81,7 +126,7 @@ class PostQueryBuilder
   end
 
   def table_for_metatag(metatag)
-    if metatag.in?(Tag::COUNT_METATAGS)
+    if metatag.in?(COUNT_METATAGS)
       metatag[/(?<table>[a-z]+)_count\z/i, :table]
     else
       nil
@@ -111,7 +156,7 @@ class PostQueryBuilder
 
   def build
     unless query_string.is_a?(Hash)
-      q = Tag.parse_query(query_string)
+      q = PostQueryBuilder.parse_query(query_string)
     end
 
     relation = Post.all
@@ -140,7 +185,7 @@ class PostQueryBuilder
     end
     relation = add_range_relation(q[:post_tag_count], "posts.tag_count", relation)
 
-    Tag::COUNT_METATAGS.each do |column|
+    COUNT_METATAGS.each do |column|
       relation = add_range_relation(q[column.to_sym], "posts.#{column}", relation)
     end
 
@@ -582,7 +627,7 @@ class PostQueryBuilder
     when "filesize_asc"
       relation = relation.order("posts.file_size ASC")
 
-    when /\A(?<column>#{Tag::COUNT_METATAGS.join("|")})(_(?<direction>asc|desc))?\z/i
+    when /\A(?<column>#{COUNT_METATAGS.join("|")})(_(?<direction>asc|desc))?\z/i
       column = $~[:column]
       direction = $~[:direction] || "desc"
       relation = relation.order(column => direction, :id => direction)
@@ -624,4 +669,492 @@ class PostQueryBuilder
 
     relation
   end
+
+  concerning :ParseMethods do
+    class_methods do
+      def scan_query(query, strip_metatags: false)
+        tagstr = query.to_s.gsub(/\u3000/, " ").strip
+        list = tagstr.scan(/-?source:".*?"/) || []
+        list += tagstr.gsub(/-?source:".*?"/, "").scan(/[^[:space:]]+/).uniq
+        list = list.map { |tag| tag.sub(/^[-~]/, "") } if strip_metatags
+        list
+      end
+
+      def normalize_query(query, normalize_aliases: true, sort: true)
+        tags = scan_query(query.to_s)
+        tags = tags.map { |t| Tag.normalize_name(t) }
+        tags = TagAlias.to_aliased(tags) if normalize_aliases
+        tags = tags.sort if sort
+        tags = tags.uniq
+        tags.join(" ")
+      end
+
+      def parse_query(query, options = {})
+        q = {}
+
+        q[:tag_count] = 0
+
+        q[:tags] = {
+          :related => [],
+          :include => [],
+          :exclude => []
+        }
+
+        scan_query(query).each do |token|
+          q[:tag_count] += 1 unless Danbooru.config.is_unlimited_tag?(token)
+
+          if token =~ /\A(#{METATAGS.join("|")}):(.+)\z/i
+            g1 = $1.downcase
+            g2 = $2
+            case g1
+            when "-user"
+              q[:uploader_id_neg] ||= []
+              user_id = User.name_to_id(g2)
+              q[:uploader_id_neg] << user_id unless user_id.blank?
+
+            when "user"
+              user_id = User.name_to_id(g2)
+              q[:uploader_id] = user_id unless user_id.blank?
+
+            when "-approver"
+              if g2 == "none"
+                q[:approver_id] = "any"
+              elsif g2 == "any"
+                q[:approver_id] = "none"
+              else
+                q[:approver_id_neg] ||= []
+                user_id = User.name_to_id(g2)
+                q[:approver_id_neg] << user_id unless user_id.blank?
+              end
+
+            when "approver"
+              if g2 == "none"
+                q[:approver_id] = "none"
+              elsif g2 == "any"
+                q[:approver_id] = "any"
+              else
+                user_id = User.name_to_id(g2)
+                q[:approver_id] = user_id unless user_id.blank?
+              end
+
+            when "flagger"
+              q[:flagger_ids] ||= []
+
+              if g2 == "none"
+                q[:flagger_ids] << "none"
+              elsif g2 == "any"
+                q[:flagger_ids] << "any"
+              else
+                user_id = User.name_to_id(g2)
+                q[:flagger_ids] << user_id unless user_id.blank?
+              end
+
+            when "-flagger"
+              if g2 == "none"
+                q[:flagger_ids] ||= []
+                q[:flagger_ids] << "any"
+              elsif g2 == "any"
+                q[:flagger_ids] ||= []
+                q[:flagger_ids] << "none"
+              else
+                q[:flagger_ids_neg] ||= []
+                user_id = User.name_to_id(g2)
+                q[:flagger_ids_neg] << user_id unless user_id.blank?
+              end
+
+            when "appealer"
+              q[:appealer_ids] ||= []
+
+              if g2 == "none"
+                q[:appealer_ids] << "none"
+              elsif g2 == "any"
+                q[:appealer_ids] << "any"
+              else
+                user_id = User.name_to_id(g2)
+                q[:appealer_ids] << user_id unless user_id.blank?
+              end
+
+            when "-appealer"
+              if g2 == "none"
+                q[:appealer_ids] ||= []
+                q[:appealer_ids] << "any"
+              elsif g2 == "any"
+                q[:appealer_ids] ||= []
+                q[:appealer_ids] << "none"
+              else
+                q[:appealer_ids_neg] ||= []
+                user_id = User.name_to_id(g2)
+                q[:appealer_ids_neg] << user_id unless user_id.blank?
+              end
+
+            when "commenter", "comm"
+              q[:commenter_ids] ||= []
+
+              if g2 == "none"
+                q[:commenter_ids] << "none"
+              elsif g2 == "any"
+                q[:commenter_ids] << "any"
+              else
+                user_id = User.name_to_id(g2)
+                q[:commenter_ids] << user_id unless user_id.blank?
+              end
+
+            when "noter"
+              q[:noter_ids] ||= []
+
+              if g2 == "none"
+                q[:noter_ids] << "none"
+              elsif g2 == "any"
+                q[:noter_ids] << "any"
+              else
+                user_id = User.name_to_id(g2)
+                q[:noter_ids] << user_id unless user_id.blank?
+              end
+
+            when "noteupdater"
+              q[:note_updater_ids] ||= []
+              user_id = User.name_to_id(g2)
+              q[:note_updater_ids] << user_id unless user_id.blank?
+
+            when "artcomm"
+              q[:artcomm_ids] ||= []
+              user_id = User.name_to_id(g2)
+              q[:artcomm_ids] << user_id unless user_id.blank?
+
+            when "disapproved"
+              q[:disapproved] ||= []
+              q[:disapproved] << g2
+
+            when "-disapproved"
+              q[:disapproved_neg] ||= []
+              q[:disapproved_neg] << g2
+
+            when "-pool"
+              q[:pool_neg] ||= []
+              q[:pool_neg] << g2
+
+            when "pool"
+              q[:pool] ||= []
+              q[:pool] << g2
+
+            when "ordpool"
+              q[:ordpool] = g2
+
+            when "-favgroup"
+              favgroup = FavoriteGroup.find_by_name_or_id!(g2, CurrentUser.user)
+              raise User::PrivilegeError unless favgroup.viewable_by?(CurrentUser.user)
+
+              q[:favgroups_neg] ||= []
+              q[:favgroups_neg] << favgroup
+
+            when "favgroup"
+              favgroup = FavoriteGroup.find_by_name_or_id!(g2, CurrentUser.user)
+              raise User::PrivilegeError unless favgroup.viewable_by?(CurrentUser.user)
+
+              q[:favgroups] ||= []
+              q[:favgroups] << favgroup
+
+            when "-fav"
+              favuser = User.find_by_name(g2)
+
+              if favuser.hide_favorites?
+                raise User::PrivilegeError.new
+              end
+
+              q[:tags][:exclude] << "fav:#{User.name_to_id(g2)}"
+
+            when "fav"
+              favuser = User.find_by_name(g2)
+
+              if favuser.hide_favorites?
+                raise User::PrivilegeError.new
+              end
+
+              q[:tags][:related] << "fav:#{User.name_to_id(g2)}"
+
+            when "ordfav"
+              user_id = User.name_to_id(g2)
+              favuser = User.find(user_id)
+
+              if favuser.hide_favorites?
+                raise User::PrivilegeError.new
+              end
+
+              q[:tags][:related] << "fav:#{user_id}"
+              q[:ordfav] = user_id
+
+            when "search"
+              q[:saved_searches] ||= []
+              q[:saved_searches] << g2
+
+            when "md5"
+              q[:md5] = g2.downcase.split(/,/)
+
+            when "-rating"
+              q[:rating_negated] = g2.downcase
+
+            when "rating"
+              q[:rating] = g2.downcase
+
+            when "-locked"
+              q[:locked_negated] = g2.downcase
+
+            when "locked"
+              q[:locked] = g2.downcase
+
+            when "id"
+              q[:post_id] = parse_helper(g2)
+
+            when "-id"
+              q[:post_id_negated] = g2.to_i
+
+            when "width"
+              q[:width] = parse_helper(g2)
+
+            when "height"
+              q[:height] = parse_helper(g2)
+
+            when "mpixels"
+              q[:mpixels] = parse_helper_fudged(g2, :float)
+
+            when "ratio"
+              q[:ratio] = parse_helper(g2, :ratio)
+
+            when "score"
+              q[:score] = parse_helper(g2)
+
+            when "favcount"
+              q[:fav_count] = parse_helper(g2)
+
+            when "filesize"
+              q[:filesize] = parse_helper_fudged(g2, :filesize)
+
+            when "source"
+              q[:source] = g2.gsub(/\A"(.*)"\Z/, '\1')
+
+            when "-source"
+              q[:source_neg] = g2.gsub(/\A"(.*)"\Z/, '\1')
+
+            when "date"
+              q[:date] = parse_helper(g2, :date)
+
+            when "age"
+              q[:age] = reverse_parse_helper(parse_helper(g2, :age))
+
+            when "tagcount"
+              q[:post_tag_count] = parse_helper(g2)
+
+            when /(#{TagCategory.short_name_regex})tags/
+              q["#{TagCategory.short_name_mapping[$1]}_tag_count".to_sym] = parse_helper(g2)
+
+            when "parent"
+              q[:parent] = g2.downcase
+
+            when "-parent"
+              if g2.downcase == "none"
+                q[:parent] = "any"
+              elsif g2.downcase == "any"
+                q[:parent] = "none"
+              else
+                q[:parent_neg_ids] ||= []
+                q[:parent_neg_ids] << g2.downcase
+              end
+
+            when "child"
+              q[:child] = g2.downcase
+
+            when "order"
+              g2 = g2.downcase
+
+              order, suffix, _tail = g2.partition(/_(asc|desc)\z/i)
+              if order.in?(COUNT_METATAG_SYNONYMS)
+                g2 = order.singularize + "_count" + suffix
+              end
+
+              q[:order] = g2
+
+            when "limit"
+              # Do nothing. The controller takes care of it.
+
+            when "-status"
+              q[:status_neg] = g2.downcase
+
+            when "status"
+              q[:status] = g2.downcase
+
+            when "embedded"
+              q[:embedded] = g2.downcase
+
+            when "filetype"
+              q[:filetype] = g2.downcase
+
+            when "-filetype"
+              q[:filetype_neg] = g2.downcase
+
+            when "pixiv_id", "pixiv"
+              if g2.downcase == "any" || g2.downcase == "none"
+                q[:pixiv_id] = g2.downcase
+              else
+                q[:pixiv_id] = parse_helper(g2)
+              end
+
+            when "upvote"
+              if CurrentUser.user.is_admin?
+                q[:upvote] = User.find_by_name(g2)
+              elsif CurrentUser.user.is_voter?
+                q[:upvote] = CurrentUser.user
+              end
+
+            when "downvote"
+              if CurrentUser.user.is_admin?
+                q[:downvote] = User.find_by_name(g2)
+              elsif CurrentUser.user.is_voter?
+                q[:downvote] = CurrentUser.user
+              end
+
+            when *COUNT_METATAGS
+              q[g1.to_sym] = parse_helper(g2)
+
+            when *COUNT_METATAG_SYNONYMS
+              g1 = "#{g1.singularize}_count"
+              q[g1.to_sym] = parse_helper(g2)
+
+            end
+
+          else
+            parse_tag(token, q[:tags])
+          end
+        end
+
+        q[:tags][:exclude] = TagAlias.to_aliased(q[:tags][:exclude])
+        q[:tags][:include] = TagAlias.to_aliased(q[:tags][:include])
+        q[:tags][:related] = TagAlias.to_aliased(q[:tags][:related])
+
+        return q
+      end
+
+      def parse_tag(tag, output)
+        if tag[0] == "-" && tag.size > 1
+          output[:exclude] << tag[1..-1].mb_chars.downcase
+
+        elsif tag[0] == "~" && tag.size > 1
+          output[:include] << tag[1..-1].mb_chars.downcase
+
+        elsif tag =~ /\*/
+          matches = Tag.name_matches(tag).select("name").limit(Danbooru.config.tag_query_limit).order("post_count DESC").map(&:name)
+          matches = ["~no_matches~"] if matches.empty?
+          output[:include] += matches
+
+        else
+          output[:related] << tag.mb_chars.downcase
+        end
+      end
+
+      def parse_cast(object, type)
+        case type
+        when :integer
+          object.to_i
+
+        when :float
+          object.to_f
+
+        when :date, :datetime
+          Time.zone.parse(object) rescue nil
+
+        when :age
+          DurationParser.parse(object).ago
+
+        when :ratio
+          object =~ /\A(\d+(?:\.\d+)?):(\d+(?:\.\d+)?)\Z/i
+
+          if $1 && $2.to_f != 0.0
+            ($1.to_f / $2.to_f).round(2)
+          else
+            object.to_f.round(2)
+          end
+
+        when :filesize
+          object =~ /\A(\d+(?:\.\d*)?|\d*\.\d+)([kKmM]?)[bB]?\Z/
+
+          size = $1.to_f
+          unit = $2
+
+          conversion_factor = case unit
+          when /m/i
+            1024 * 1024
+          when /k/i
+            1024
+          else
+            1
+          end
+
+          (size * conversion_factor).to_i
+        end
+      end
+
+      def parse_helper(range, type = :integer)
+        # "1", "0.5", "5.", ".5":
+        # (-?(\d+(\.\d*)?|\d*\.\d+))
+        case range
+        when /\A(.+?)\.\.(.+)/
+          return [:between, parse_cast($1, type), parse_cast($2, type)]
+
+        when /\A<=(.+)/, /\A\.\.(.+)/
+          return [:lte, parse_cast($1, type)]
+
+        when /\A<(.+)/
+          return [:lt, parse_cast($1, type)]
+
+        when /\A>=(.+)/, /\A(.+)\.\.\Z/
+          return [:gte, parse_cast($1, type)]
+
+        when /\A>(.+)/
+          return [:gt, parse_cast($1, type)]
+
+        when /[, ]/
+          return [:in, range.split(/[, ]+/).map {|x| parse_cast(x, type)}]
+
+        else
+          return [:eq, parse_cast(range, type)]
+
+        end
+      end
+
+      def parse_helper_fudged(range, type)
+        result = parse_helper(range, type)
+        # Don't fudge the filesize when searching filesize:123b or filesize:123.
+        if result[0] == :eq && type == :filesize && range !~ /[km]b?\Z/i
+          result
+        elsif result[0] == :eq
+          new_min = (result[1] * 0.95).to_i
+          new_max = (result[1] * 1.05).to_i
+          [:between, new_min, new_max]
+        else
+          result
+        end
+      end
+
+      def reverse_parse_helper(array)
+        case array[0]
+        when :between
+          [:between, *array[1..-1].reverse]
+
+        when :lte
+          [:gte, *array[1..-1]]
+
+        when :lt
+          [:gt, *array[1..-1]]
+
+        when :gte
+          [:lte, *array[1..-1]]
+
+        when :gt
+          [:lt, *array[1..-1]]
+
+        else
+          array
+        end
+      end
+    end
+  end
 end
diff --git a/app/logical/post_sets/post.rb b/app/logical/post_sets/post.rb
index a5347d7fe..0470fba84 100644
--- a/app/logical/post_sets/post.rb
+++ b/app/logical/post_sets/post.rb
@@ -4,7 +4,7 @@ module PostSets
     attr_reader :tag_array, :page, :raw, :random, :post_count, :format
 
     def initialize(tags, page = 1, per_page = nil, raw: false, random: false, format: "html")
-      @tag_array = Tag.scan_query(tags)
+      @tag_array = PostQueryBuilder.scan_query(tags)
       @page = page
       @per_page = per_page
       @raw = raw.to_s.truthy?
diff --git a/app/logical/tag_name_validator.rb b/app/logical/tag_name_validator.rb
index 9cbcecad3..c890f1695 100644
--- a/app/logical/tag_name_validator.rb
+++ b/app/logical/tag_name_validator.rb
@@ -21,7 +21,7 @@ class TagNameValidator < ActiveModel::EachValidator
       record.errors[attribute] << "'#{value}' cannot contain non-printable characters"
     when /[^[:ascii:]]/
       record.errors[attribute] << "'#{value}' must consist of only ASCII characters"
-    when /\A(#{Tag::METATAGS.join("|")}):(.+)\z/i
+    when /\A(#{PostQueryBuilder::METATAGS.join("|")}):(.+)\z/i
       record.errors[attribute] << "'#{value}' cannot begin with '#{$1}:'"
     when /\A(#{Tag.categories.regexp}):(.+)\z/i
       record.errors[attribute] << "'#{value}' cannot begin with '#{$1}:'"
diff --git a/app/models/post.rb b/app/models/post.rb
index 21cf08d1c..a0f0071d8 100644
--- a/app/models/post.rb
+++ b/app/models/post.rb
@@ -522,11 +522,11 @@ class Post < ApplicationRecord
 
   module TagMethods
     def tag_array
-      @tag_array ||= Tag.scan_tags(tag_string)
+      @tag_array ||= PostQueryBuilder.scan_query(tag_string)
     end
 
     def tag_array_was
-      @tag_array_was ||= Tag.scan_tags(tag_string_in_database.presence || tag_string_before_last_save || "")
+      @tag_array_was ||= PostQueryBuilder.scan_query(tag_string_in_database.presence || tag_string_before_last_save || "")
     end
 
     def tags
@@ -590,7 +590,7 @@ class Post < ApplicationRecord
         # then try to merge the tag changes together.
         current_tags = tag_array_was
         new_tags = tag_array
-        old_tags = Tag.scan_tags(old_tag_string)
+        old_tags = PostQueryBuilder.scan_query(old_tag_string)
 
         kept_tags = current_tags & new_tags
         @removed_tags = old_tags - kept_tags
@@ -627,7 +627,7 @@ class Post < ApplicationRecord
     end
 
     def normalize_tags
-      normalized_tags = Tag.scan_tags(tag_string)
+      normalized_tags = PostQueryBuilder.scan_query(tag_string)
       normalized_tags = apply_casesensitive_metatags(normalized_tags)
       normalized_tags = normalized_tags.map(&:downcase)
       normalized_tags = filter_metatags(normalized_tags)
@@ -1058,7 +1058,7 @@ class Post < ApplicationRecord
       tags = tags.to_s
       tags += " rating:s" if CurrentUser.safe_mode?
       tags += " -status:deleted" if CurrentUser.hide_deleted_posts? && !Tag.has_metatag?(tags, "status", "-status")
-      tags = Tag.normalize_query(tags)
+      tags = PostQueryBuilder.normalize_query(tags)
 
       # Optimize some cases. these are just estimates but at these
       # quantities being off by a few hundred doesn't matter much
diff --git a/app/models/saved_search.rb b/app/models/saved_search.rb
index 22f6c6151..548201648 100644
--- a/app/models/saved_search.rb
+++ b/app/models/saved_search.rb
@@ -139,18 +139,18 @@ class SavedSearch < ApplicationRecord
           .where(user_id: user_id)
           .labeled(label)
           .pluck(:query)
-          .map {|x| Tag.normalize_query(x, sort: true)}
+          .map {|x| PostQueryBuilder.normalize_query(x, sort: true)}
           .sort
           .uniq
       end
     end
 
     def normalized_query
-      Tag.normalize_query(query, sort: true)
+      PostQueryBuilder.normalize_query(query, sort: true)
     end
 
     def normalize_query
-      self.query = Tag.normalize_query(query, sort: false)
+      self.query = PostQueryBuilder.normalize_query(query, sort: false)
     end
   end
 
diff --git a/app/models/tag.rb b/app/models/tag.rb
index b283e42ee..5f78f26a8 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -1,51 +1,4 @@
 class Tag < ApplicationRecord
-  COUNT_METATAGS = %w[
-    comment_count deleted_comment_count active_comment_count
-    note_count deleted_note_count active_note_count
-    flag_count resolved_flag_count unresolved_flag_count
-    child_count deleted_child_count active_child_count
-    pool_count deleted_pool_count active_pool_count series_pool_count collection_pool_count
-    appeal_count approval_count replacement_count
-  ]
-
-  # allow e.g. `deleted_comments` as a synonym for `deleted_comment_count`
-  COUNT_METATAG_SYNONYMS = COUNT_METATAGS.map { |str| str.delete_suffix("_count").pluralize }
-
-  METATAGS = %w[
-    -user user -approver approver commenter comm noter noteupdater artcomm
-    -pool pool ordpool -favgroup favgroup -fav fav ordfav md5 -rating rating
-    -locked locked width height mpixels ratio score favcount filesize source
-    -source id -id date age order limit -status status tagcount parent -parent
-    child pixiv_id pixiv search upvote downvote filetype -filetype flagger
-    -flagger appealer -appealer disapproved -disapproved embedded
-  ] + TagCategory.short_name_list.map {|x| "#{x}tags"} + COUNT_METATAGS + COUNT_METATAG_SYNONYMS
-
-  SUBQUERY_METATAGS = %w[commenter comm noter noteupdater artcomm flagger -flagger appealer -appealer]
-
-  ORDER_METATAGS = %w[
-    id id_desc
-    score score_asc
-    favcount favcount_asc
-    created_at created_at_asc
-    change change_asc
-    comment comment_asc
-    comment_bumped comment_bumped_asc
-    note note_asc
-    artcomm artcomm_asc
-    mpixels mpixels_asc
-    portrait landscape
-    filesize filesize_asc
-    tagcount tagcount_asc
-    rank
-    curated
-    modqueue
-    random
-    custom
-  ] +
-    COUNT_METATAGS +
-    COUNT_METATAG_SYNONYMS.flat_map { |str| [str, "#{str}_asc"] } +
-    TagCategory.short_name_list.flat_map { |str| ["#{str}tags", "#{str}tags_asc"] }
-
   has_one :wiki_page, :foreign_key => "title", :primary_key => "name"
   has_one :artist, :foreign_key => "name", :primary_key => "name"
   has_one :antecedent_alias, -> {active}, :class_name => "TagAlias", :foreign_key => "antecedent_name", :primary_key => "name"
@@ -268,169 +221,17 @@ class Tag < ApplicationRecord
   end
 
   module ParseMethods
-    def normalize(query)
-      query.to_s.gsub(/\u3000/, " ").strip
-    end
-
-    def normalize_query(query, normalize_aliases: true, sort: true)
-      tags = Tag.scan_query(query.to_s)
-      tags = tags.map { |t| Tag.normalize_name(t) }
-      tags = TagAlias.to_aliased(tags) if normalize_aliases
-      tags = tags.sort if sort
-      tags = tags.uniq
-      tags.join(" ")
-    end
-
-    def scan_query(query)
-      tagstr = normalize(query)
-      list = tagstr.scan(/-?source:".*?"/) || []
-      list + tagstr.gsub(/-?source:".*?"/, "").scan(/[^[:space:]]+/).uniq
-    end
-
-    def scan_tags(tags, options = {})
-      tagstr = normalize(tags)
-      list = tagstr.scan(/source:".*?"/) || []
-      list += tagstr.gsub(/source:".*?"/, "").scan(/[^[:space:]]+/).uniq
-      if options[:strip_metatags]
-        list = list.map {|x| x.sub(/^[-~]/, "")}
-      end
-      list
-    end
-
-    def parse_cast(object, type)
-      case type
-      when :integer
-        object.to_i
-
-      when :float
-        object.to_f
-
-      when :date, :datetime
-        Time.zone.parse(object) rescue nil
-
-      when :age
-        DurationParser.parse(object).ago
-
-      when :ratio
-        object =~ /\A(\d+(?:\.\d+)?):(\d+(?:\.\d+)?)\Z/i
-
-        if $1 && $2.to_f != 0.0
-          ($1.to_f / $2.to_f).round(2)
-        else
-          object.to_f.round(2)
-        end
-
-      when :filesize
-        object =~ /\A(\d+(?:\.\d*)?|\d*\.\d+)([kKmM]?)[bB]?\Z/
-
-        size = $1.to_f
-        unit = $2
-
-        conversion_factor = case unit
-        when /m/i
-          1024 * 1024
-        when /k/i
-          1024
-        else
-          1
-        end
-
-        (size * conversion_factor).to_i
-      end
-    end
-
-    def parse_helper(range, type = :integer)
-      # "1", "0.5", "5.", ".5":
-      # (-?(\d+(\.\d*)?|\d*\.\d+))
-      case range
-      when /\A(.+?)\.\.(.+)/
-        return [:between, parse_cast($1, type), parse_cast($2, type)]
-
-      when /\A<=(.+)/, /\A\.\.(.+)/
-        return [:lte, parse_cast($1, type)]
-
-      when /\A<(.+)/
-        return [:lt, parse_cast($1, type)]
-
-      when /\A>=(.+)/, /\A(.+)\.\.\Z/
-        return [:gte, parse_cast($1, type)]
-
-      when /\A>(.+)/
-        return [:gt, parse_cast($1, type)]
-
-      when /[, ]/
-        return [:in, range.split(/[, ]+/).map {|x| parse_cast(x, type)}]
-
-      else
-        return [:eq, parse_cast(range, type)]
-
-      end
-    end
-
-    def parse_helper_fudged(range, type)
-      result = parse_helper(range, type)
-      # Don't fudge the filesize when searching filesize:123b or filesize:123.
-      if result[0] == :eq && type == :filesize && range !~ /[km]b?\Z/i
-        result
-      elsif result[0] == :eq
-        new_min = (result[1] * 0.95).to_i
-        new_max = (result[1] * 1.05).to_i
-        [:between, new_min, new_max]
-      else
-        result
-      end
-    end
-
-    def reverse_parse_helper(array)
-      case array[0]
-      when :between
-        [:between, *array[1..-1].reverse]
-
-      when :lte
-        [:gte, *array[1..-1]]
-
-      when :lt
-        [:gt, *array[1..-1]]
-
-      when :gte
-        [:lte, *array[1..-1]]
-
-      when :gt
-        [:lt, *array[1..-1]]
-
-      else
-        array
-      end
-    end
-
-    def parse_tag(tag, output)
-      if tag[0] == "-" && tag.size > 1
-        output[:exclude] << tag[1..-1].mb_chars.downcase
-
-      elsif tag[0] == "~" && tag.size > 1
-        output[:include] << tag[1..-1].mb_chars.downcase
-
-      elsif tag =~ /\*/
-        matches = Tag.name_matches(tag).select("name").limit(Danbooru.config.tag_query_limit).order("post_count DESC").map(&:name)
-        matches = ["~no_matches~"] if matches.empty?
-        output[:include] += matches
-
-      else
-        output[:related] << tag.mb_chars.downcase
-      end
-    end
-
     # true if query is a single "simple" tag (not a metatag, negated tag, or wildcard tag).
     def is_simple_tag?(query)
       is_single_tag?(query) && !is_metatag?(query) && !is_negated_tag?(query) && !is_optional_tag?(query) && !is_wildcard_tag?(query)
     end
 
     def is_single_tag?(query)
-      scan_query(query).size == 1
+      PostQueryBuilder.scan_query(query).size == 1
     end
 
     def is_metatag?(tag)
-      has_metatag?(tag, *METATAGS)
+      has_metatag?(tag, *PostQueryBuilder::METATAGS)
     end
 
     def is_negated_tag?(tag)
@@ -448,357 +249,9 @@ class Tag < ApplicationRecord
     def has_metatag?(tags, *metatags)
       return nil if tags.blank?
 
-      tags = scan_query(tags.to_str) if tags.respond_to?(:to_str)
+      tags = PostQueryBuilder.scan_query(tags.to_str) if tags.respond_to?(:to_str)
       tags.grep(/\A(?:#{metatags.map(&:to_s).join("|")}):(.+)\z/i) { $1 }.first
     end
-
-    def parse_query(query, options = {})
-      q = {}
-
-      q[:tag_count] = 0
-
-      q[:tags] = {
-        :related => [],
-        :include => [],
-        :exclude => []
-      }
-
-      scan_query(query).each do |token|
-        q[:tag_count] += 1 unless Danbooru.config.is_unlimited_tag?(token)
-
-        if token =~ /\A(#{METATAGS.join("|")}):(.+)\z/i
-          g1 = $1.downcase
-          g2 = $2
-          case g1
-          when "-user"
-            q[:uploader_id_neg] ||= []
-            user_id = User.name_to_id(g2)
-            q[:uploader_id_neg] << user_id unless user_id.blank?
-
-          when "user"
-            user_id = User.name_to_id(g2)
-            q[:uploader_id] = user_id unless user_id.blank?
-
-          when "-approver"
-            if g2 == "none"
-              q[:approver_id] = "any"
-            elsif g2 == "any"
-              q[:approver_id] = "none"
-            else
-              q[:approver_id_neg] ||= []
-              user_id = User.name_to_id(g2)
-              q[:approver_id_neg] << user_id unless user_id.blank?
-            end
-
-          when "approver"
-            if g2 == "none"
-              q[:approver_id] = "none"
-            elsif g2 == "any"
-              q[:approver_id] = "any"
-            else
-              user_id = User.name_to_id(g2)
-              q[:approver_id] = user_id unless user_id.blank?
-            end
-
-          when "flagger"
-            q[:flagger_ids] ||= []
-
-            if g2 == "none"
-              q[:flagger_ids] << "none"
-            elsif g2 == "any"
-              q[:flagger_ids] << "any"
-            else
-              user_id = User.name_to_id(g2)
-              q[:flagger_ids] << user_id unless user_id.blank?
-            end
-
-          when "-flagger"
-            if g2 == "none"
-              q[:flagger_ids] ||= []
-              q[:flagger_ids] << "any"
-            elsif g2 == "any"
-              q[:flagger_ids] ||= []
-              q[:flagger_ids] << "none"
-            else
-              q[:flagger_ids_neg] ||= []
-              user_id = User.name_to_id(g2)
-              q[:flagger_ids_neg] << user_id unless user_id.blank?
-            end
-
-          when "appealer"
-            q[:appealer_ids] ||= []
-
-            if g2 == "none"
-              q[:appealer_ids] << "none"
-            elsif g2 == "any"
-              q[:appealer_ids] << "any"
-            else
-              user_id = User.name_to_id(g2)
-              q[:appealer_ids] << user_id unless user_id.blank?
-            end
-
-          when "-appealer"
-            if g2 == "none"
-              q[:appealer_ids] ||= []
-              q[:appealer_ids] << "any"
-            elsif g2 == "any"
-              q[:appealer_ids] ||= []
-              q[:appealer_ids] << "none"
-            else
-              q[:appealer_ids_neg] ||= []
-              user_id = User.name_to_id(g2)
-              q[:appealer_ids_neg] << user_id unless user_id.blank?
-            end
-
-          when "commenter", "comm"
-            q[:commenter_ids] ||= []
-
-            if g2 == "none"
-              q[:commenter_ids] << "none"
-            elsif g2 == "any"
-              q[:commenter_ids] << "any"
-            else
-              user_id = User.name_to_id(g2)
-              q[:commenter_ids] << user_id unless user_id.blank?
-            end
-
-          when "noter"
-            q[:noter_ids] ||= []
-
-            if g2 == "none"
-              q[:noter_ids] << "none"
-            elsif g2 == "any"
-              q[:noter_ids] << "any"
-            else
-              user_id = User.name_to_id(g2)
-              q[:noter_ids] << user_id unless user_id.blank?
-            end
-
-          when "noteupdater"
-            q[:note_updater_ids] ||= []
-            user_id = User.name_to_id(g2)
-            q[:note_updater_ids] << user_id unless user_id.blank?
-
-          when "artcomm"
-            q[:artcomm_ids] ||= []
-            user_id = User.name_to_id(g2)
-            q[:artcomm_ids] << user_id unless user_id.blank?
-
-          when "disapproved"
-            q[:disapproved] ||= []
-            q[:disapproved] << g2
-
-          when "-disapproved"
-            q[:disapproved_neg] ||= []
-            q[:disapproved_neg] << g2
-
-          when "-pool"
-            q[:pool_neg] ||= []
-            q[:pool_neg] << g2
-
-          when "pool"
-            q[:pool] ||= []
-            q[:pool] << g2
-
-          when "ordpool"
-            q[:ordpool] = g2
-
-          when "-favgroup"
-            favgroup = FavoriteGroup.find_by_name_or_id!(g2, CurrentUser.user)
-            raise User::PrivilegeError unless favgroup.viewable_by?(CurrentUser.user)
-
-            q[:favgroups_neg] ||= []
-            q[:favgroups_neg] << favgroup
-
-          when "favgroup"
-            favgroup = FavoriteGroup.find_by_name_or_id!(g2, CurrentUser.user)
-            raise User::PrivilegeError unless favgroup.viewable_by?(CurrentUser.user)
-
-            q[:favgroups] ||= []
-            q[:favgroups] << favgroup
-
-          when "-fav"
-            favuser = User.find_by_name(g2)
-
-            if favuser.hide_favorites?
-              raise User::PrivilegeError.new
-            end
-
-            q[:tags][:exclude] << "fav:#{User.name_to_id(g2)}"
-
-          when "fav"
-            favuser = User.find_by_name(g2)
-
-            if favuser.hide_favorites?
-              raise User::PrivilegeError.new
-            end
-
-            q[:tags][:related] << "fav:#{User.name_to_id(g2)}"
-
-          when "ordfav"
-            user_id = User.name_to_id(g2)
-            favuser = User.find(user_id)
-
-            if favuser.hide_favorites?
-              raise User::PrivilegeError.new
-            end
-
-            q[:tags][:related] << "fav:#{user_id}"
-            q[:ordfav] = user_id
-
-          when "search"
-            q[:saved_searches] ||= []
-            q[:saved_searches] << g2
-
-          when "md5"
-            q[:md5] = g2.downcase.split(/,/)
-
-          when "-rating"
-            q[:rating_negated] = g2.downcase
-
-          when "rating"
-            q[:rating] = g2.downcase
-
-          when "-locked"
-            q[:locked_negated] = g2.downcase
-
-          when "locked"
-            q[:locked] = g2.downcase
-
-          when "id"
-            q[:post_id] = parse_helper(g2)
-
-          when "-id"
-            q[:post_id_negated] = g2.to_i
-
-          when "width"
-            q[:width] = parse_helper(g2)
-
-          when "height"
-            q[:height] = parse_helper(g2)
-
-          when "mpixels"
-            q[:mpixels] = parse_helper_fudged(g2, :float)
-
-          when "ratio"
-            q[:ratio] = parse_helper(g2, :ratio)
-
-          when "score"
-            q[:score] = parse_helper(g2)
-
-          when "favcount"
-            q[:fav_count] = parse_helper(g2)
-
-          when "filesize"
-            q[:filesize] = parse_helper_fudged(g2, :filesize)
-
-          when "source"
-            q[:source] = g2.gsub(/\A"(.*)"\Z/, '\1')
-
-          when "-source"
-            q[:source_neg] = g2.gsub(/\A"(.*)"\Z/, '\1')
-
-          when "date"
-            q[:date] = parse_helper(g2, :date)
-
-          when "age"
-            q[:age] = reverse_parse_helper(parse_helper(g2, :age))
-
-          when "tagcount"
-            q[:post_tag_count] = parse_helper(g2)
-
-          when /(#{TagCategory.short_name_regex})tags/
-            q["#{TagCategory.short_name_mapping[$1]}_tag_count".to_sym] = parse_helper(g2)
-
-          when "parent"
-            q[:parent] = g2.downcase
-
-          when "-parent"
-            if g2.downcase == "none"
-              q[:parent] = "any"
-            elsif g2.downcase == "any"
-              q[:parent] = "none"
-            else
-              q[:parent_neg_ids] ||= []
-              q[:parent_neg_ids] << g2.downcase
-            end
-
-          when "child"
-            q[:child] = g2.downcase
-
-          when "order"
-            g2 = g2.downcase
-
-            order, suffix, _tail = g2.partition(/_(asc|desc)\z/i)
-            if order.in?(COUNT_METATAG_SYNONYMS)
-              g2 = order.singularize + "_count" + suffix
-            end
-
-            q[:order] = g2
-
-          when "limit"
-            # Do nothing. The controller takes care of it.
-
-          when "-status"
-            q[:status_neg] = g2.downcase
-
-          when "status"
-            q[:status] = g2.downcase
-
-          when "embedded"
-            q[:embedded] = g2.downcase
-
-          when "filetype"
-            q[:filetype] = g2.downcase
-
-          when "-filetype"
-            q[:filetype_neg] = g2.downcase
-
-          when "pixiv_id", "pixiv"
-            if g2.downcase == "any" || g2.downcase == "none"
-              q[:pixiv_id] = g2.downcase
-            else
-              q[:pixiv_id] = parse_helper(g2)
-            end
-
-          when "upvote"
-            if CurrentUser.user.is_admin?
-              q[:upvote] = User.find_by_name(g2)
-            elsif CurrentUser.user.is_voter?
-              q[:upvote] = CurrentUser.user
-            end
-
-          when "downvote"
-            if CurrentUser.user.is_admin?
-              q[:downvote] = User.find_by_name(g2)
-            elsif CurrentUser.user.is_voter?
-              q[:downvote] = CurrentUser.user
-            end
-
-          when *COUNT_METATAGS
-            q[g1.to_sym] = parse_helper(g2)
-
-          when *COUNT_METATAG_SYNONYMS
-            g1 = "#{g1.singularize}_count"
-            q[g1.to_sym] = parse_helper(g2)
-
-          end
-
-        else
-          parse_tag(token, q[:tags])
-        end
-      end
-
-      normalize_tags_in_query(q)
-
-      return q
-    end
-
-    def normalize_tags_in_query(query_hash)
-      query_hash[:tags][:exclude] = TagAlias.to_aliased(query_hash[:tags][:exclude])
-      query_hash[:tags][:include] = TagAlias.to_aliased(query_hash[:tags][:include])
-      query_hash[:tags][:related] = TagAlias.to_aliased(query_hash[:tags][:related])
-    end
   end
 
   module SearchMethods
diff --git a/test/unit/post_test.rb b/test/unit/post_test.rb
index b64ee78ff..52d332bf9 100644
--- a/test/unit/post_test.rb
+++ b/test/unit/post_test.rb
@@ -1430,7 +1430,7 @@ class PostTest < ActiveSupport::TestCase
 
           # final should be <aaa>, <bbb>, <ddd>, <eee>
           final_post = Post.find(post.id)
-          assert_equal(%w(aaa bbb ddd eee), Tag.scan_tags(final_post.tag_string).sort)
+          assert_equal(%w(aaa bbb ddd eee), PostQueryBuilder.scan_query(final_post.tag_string).sort)
         end
 
         should "merge any tag changes that were made after loading the initial set of tags part 2" do
@@ -1453,7 +1453,7 @@ class PostTest < ActiveSupport::TestCase
 
           # final should be <aaa>, <bbb>, <ddd>, <eee>
           final_post = Post.find(post.id)
-          assert_equal(%w(aaa bbb ddd eee), Tag.scan_tags(final_post.tag_string).sort)
+          assert_equal(%w(aaa bbb ddd eee), PostQueryBuilder.scan_query(final_post.tag_string).sort)
         end
 
         should "merge any parent, source, and rating changes that were made after loading the initial set" do
diff --git a/test/unit/tag_test.rb b/test/unit/tag_test.rb
index 83022be57..04ef63932 100644
--- a/test/unit/tag_test.rb
+++ b/test/unit/tag_test.rb
@@ -93,37 +93,36 @@ class TagTest < ActiveSupport::TestCase
 
   context "A tag parser" do
     should "scan a query" do
-      assert_equal(%w(aaa bbb), Tag.scan_query("aaa bbb"))
-      assert_equal(%w(~AAa -BBB* -bbb*), Tag.scan_query("~AAa -BBB* -bbb*"))
+      assert_equal(%w(aaa bbb), PostQueryBuilder.scan_query("aaa bbb"))
+      assert_equal(%w(~AAa -BBB* -bbb*), PostQueryBuilder.scan_query("~AAa -BBB* -bbb*"))
     end
 
     should "not strip out valid characters when scanning" do
-      assert_equal(%w(aaa bbb), Tag.scan_tags("aaa bbb"))
-      assert_equal(%w(favgroup:yondemasu_yo,_azazel-san. pool:ichigo_100%), Tag.scan_tags("favgroup:yondemasu_yo,_azazel-san. pool:ichigo_100%"))
+      assert_equal(%w(aaa bbb), PostQueryBuilder.scan_query("aaa bbb"))
+      assert_equal(%w(favgroup:yondemasu_yo,_azazel-san. pool:ichigo_100%), PostQueryBuilder.scan_query("favgroup:yondemasu_yo,_azazel-san. pool:ichigo_100%"))
     end
 
     should "cast values" do
-      assert_equal(2048, Tag.parse_cast("2kb", :filesize))
-      assert_equal(2097152, Tag.parse_cast("2m", :filesize))
-      assert_nothing_raised {Tag.parse_cast("2009-01-01", :date)}
-      assert_nothing_raised {Tag.parse_cast("1234", :integer)}
-      assert_nothing_raised {Tag.parse_cast("1234.56", :float)}
+      assert_equal(2048, PostQueryBuilder.parse_cast("2kb", :filesize))
+      assert_equal(2097152, PostQueryBuilder.parse_cast("2m", :filesize))
+      assert_nothing_raised {PostQueryBuilder.parse_cast("2009-01-01", :date)}
+      assert_nothing_raised {PostQueryBuilder.parse_cast("1234", :integer)}
+      assert_nothing_raised {PostQueryBuilder.parse_cast("1234.56", :float)}
     end
 
     should "parse a query" do
       tag1 = FactoryBot.create(:tag, :name => "abc")
       tag2 = FactoryBot.create(:tag, :name => "acb")
 
-      assert_equal(["abc"], Tag.parse_query("md5:abc")[:md5])
-      assert_equal([:between, 1, 2], Tag.parse_query("id:1..2")[:post_id])
-      assert_equal([:gte, 1], Tag.parse_query("id:1..")[:post_id])
-      assert_equal([:lte, 2], Tag.parse_query("id:..2")[:post_id])
-      assert_equal([:gt, 2], Tag.parse_query("id:>2")[:post_id])
-      assert_equal([:lt, 3], Tag.parse_query("id:<3")[:post_id])
-      assert_equal([:lt, 3], Tag.parse_query("ID:<3")[:post_id])
+      assert_equal(["abc"], PostQueryBuilder.parse_query("md5:abc")[:md5])
+      assert_equal([:between, 1, 2], PostQueryBuilder.parse_query("id:1..2")[:post_id])
+      assert_equal([:gte, 1], PostQueryBuilder.parse_query("id:1..")[:post_id])
+      assert_equal([:lte, 2], PostQueryBuilder.parse_query("id:..2")[:post_id])
+      assert_equal([:gt, 2], PostQueryBuilder.parse_query("id:>2")[:post_id])
+      assert_equal([:lt, 3], PostQueryBuilder.parse_query("id:<3")[:post_id])
+      assert_equal([:lt, 3], PostQueryBuilder.parse_query("ID:<3")[:post_id])
 
-      Tag.expects(:normalize_tags_in_query).returns(nil)
-      assert_equal(["acb"], Tag.parse_query("a*b")[:tags][:include])
+      assert_equal(["acb"], PostQueryBuilder.parse_query("a*b")[:tags][:include])
     end
 
     should "parse single tags correctly" do
@@ -238,7 +237,7 @@ class TagTest < ActiveSupport::TestCase
       should_not allow_value("東方").for(:name).on(:create)
       should_not allow_value("FAV:blah").for(:name).on(:create)
 
-      metatags = Tag::METATAGS + TagCategory.mapping.keys
+      metatags = PostQueryBuilder::METATAGS + TagCategory.mapping.keys
       metatags.each do |metatag|
         should_not allow_value("#{metatag}:foo").for(:name).on(:create)
       end