diff --git a/app/blueprints/api/v1/error_blueprint.rb b/app/blueprints/api/v1/error_blueprint.rb
index 78a431a..29796c0 100644
--- a/app/blueprints/api/v1/error_blueprint.rb
+++ b/app/blueprints/api/v1/error_blueprint.rb
@@ -14,6 +14,10 @@ module Api
       field :errors, if: ->(_field_name, _error, options) { options.key?(:exception) } do |_, options|
         options[:exception]
       end
+
+      field :errors, if: ->(_field_name, object, options) { options.key?(:errors) } do |_, options|
+        options[:errors]
+      end
     end
   end
 end
diff --git a/app/models/grid_character.rb b/app/models/grid_character.rb
index 2e3e16b..e60bcf9 100644
--- a/app/models/grid_character.rb
+++ b/app/models/grid_character.rb
@@ -3,6 +3,42 @@
 class GridCharacter < ApplicationRecord
   belongs_to :party
 
+  validate :awakening_level, on: :update
+  validate :transcendence, on: :update
+  validate :over_mastery_attack, on: :update
+  validate :over_mastery_hp, on: :update
+  validate :over_mastery_attack_matches_hp, on: :update
+
+  def awakening_level
+    unless awakening.nil?
+      errors.add(:awakening, 'awakening level too low') if awakening["level"] < 1
+      errors.add(:awakening, 'awakening level too high') if awakening["level"] > 9
+    end
+  end
+
+  def transcendence
+    errors.add(:transcendence_step, 'character has no transcendence') if transcendence_step > 0 && !character.ulb
+    errors.add(:transcendence_step, 'transcendence step too high') if transcendence_step > 5 && character.ulb
+    errors.add(:transcendence_step, 'transcendence step too low') if transcendence_step < 0 && character.ulb
+
+  end
+
+  def over_mastery_attack
+    errors.add(:ring1, 'invalid value') unless ring1["modifier"].nil? || atk_values.include?(ring1["strength"])
+  end
+
+  def over_mastery_hp
+    unless ring2["modifier"].nil?
+      errors.add(:ring2, 'invalid value') unless hp_values.include?(ring2["strength"])
+    end
+  end
+
+  def over_mastery_attack_matches_hp
+    unless ring1[:modifier].nil? && ring2[:modifier].nil?
+      errors.add(:over_mastery, 'over mastery attack and hp values do not match') unless ring2[:strength] == (ring1[:strength] / 2)
+    end
+  end
+
   def character
     Character.find(character_id)
   end
@@ -10,4 +46,14 @@ class GridCharacter < ApplicationRecord
   def blueprint
     GridCharacterBlueprint
   end
+
+  private
+
+  def atk_values
+    [300, 600, 900, 1200, 1500, 1800, 2100, 2400, 2700, 3000]
+  end
+
+  def hp_values
+    [150, 300, 450, 600, 750, 900, 1050, 1200, 1350, 1500]
+  end
 end