diff --git a/lib/prism/orm/type_casting.rb b/lib/prism/orm/type_casting.rb
new file mode 100644
index 0000000..4dcc4f7
--- /dev/null
+++ b/lib/prism/orm/type_casting.rb
@@ -0,0 +1,91 @@
+require 'time'
+
+module Prism
+  module Orm
+    # ActiveModel::Type-lite: coerces a raw value (almost always a String,
+    # since every value that ever crosses an HTTP request - query string,
+    # form body, JSON string fields typed as numbers-in-quotes - arrives as
+    # one) into the Ruby type an attribute is declared to hold.
+    #
+    # Kept deliberately separate from Store/Migration's column *names*:
+    # a migration's `t.integer :views` has never done anything with the
+    # type beyond documenting intent (TableDefinition#column discards it),
+    # and this module does not change that. Casting here is opt-in per
+    # attribute via `Attributes.attribute` - it does not infer behavior
+    # from a migration's declared column type.
+    module TypeCasting
+      class InvalidCast < StandardError; end
+
+      TRUE_STRINGS = %w[1 t true y yes on].freeze
+      FALSE_STRINGS = %w[0 f false n no off].freeze
+
+      module_function
+
+      def cast(type, value)
+        return nil if value.nil?
+
+        case type
+        when :string, :text then cast_string(value)
+        when :integer then cast_integer(value)
+        when :float then cast_float(value)
+        when :boolean then cast_boolean(value)
+        when :datetime then cast_datetime(value)
+        else raise ArgumentError, "unknown attribute type #{type.inspect}"
+        end
+      end
+
+      def cast_string(value)
+        value.is_a?(String) ? value : value.to_s
+      end
+
+      # Blank input ("" left in an optional numeric form field) casts to
+      # nil rather than 0 - the two mean different things (unknown vs.
+      # zero) and collapsing them would silently corrupt any numericality
+      # validation or aggregate downstream. Anything non-blank that is not
+      # a real integer is a boundary violation (malformed request/API
+      # misuse), not a value worth guessing at, so it raises loudly - the
+      # same posture this ORM already takes for StaleObjectError/
+      # UniqueConstraintViolation rather than swallowing the problem.
+      def cast_integer(value)
+        return value if value.is_a?(Integer)
+        return value.to_i if value.is_a?(Numeric)
+        str = value.to_s.strip
+        return nil if str.empty?
+        Integer(str, 10)
+      rescue ArgumentError
+        raise InvalidCast, "#{value.inspect} is not a valid :integer"
+      end
+
+      def cast_float(value)
+        return value if value.is_a?(Float)
+        return value.to_f if value.is_a?(Numeric)
+        str = value.to_s.strip
+        return nil if str.empty?
+        Float(str)
+      rescue ArgumentError
+        raise InvalidCast, "#{value.inspect} is not a valid :float"
+      end
+
+      # true/false pass through untouched (including from a previously-cast
+      # attribute re-read through the getter). Recognized string/integer
+      # forms map case-insensitively; anything else raises rather than
+      # defaulting to Ruby's "anything non-nil/false is truthy", which
+      # would silently turn a typo'd param value into `true`.
+      def cast_boolean(value)
+        return value if value == true || value == false
+        token = value.is_a?(String) ? value.strip.downcase : value.to_s
+        return true if TRUE_STRINGS.include?(token)
+        return false if FALSE_STRINGS.include?(token)
+        raise InvalidCast, "#{value.inspect} is not a valid :boolean"
+      end
+
+      def cast_datetime(value)
+        return value if value.is_a?(Time)
+        return value.to_time if value.is_a?(Date) || value.is_a?(DateTime)
+        Time.parse(value.to_s)
+      rescue ArgumentError
+        raise InvalidCast, "#{value.inspect} is not a valid :datetime"
+      end
+    end
+  end
+end
diff --git a/lib/prism/orm/validatable.rb b/lib/prism/orm/validatable.rb
index 32c3325..3513a6f 100644
--- a/lib/prism/orm/validatable.rb
+++ b/lib/prism/orm/validatable.rb
@@ -10,11 +10,34 @@ module Prism
           @validators ||= []
         end
 
+        def custom_validators
+          @custom_validators ||= []
+        end
+
         def validates(*attributes, **rules)
           attributes.each do |attribute|
             rules.each { |kind, config| validators << { attribute: attribute, kind: kind, config: config } }
           end
         end
+
+        def validates_numericality_of(*attributes, **options)
+          validates(*attributes, numericality: options)
+        end
+
+        def validates_inclusion_of(*attributes, **options)
+          validates(*attributes, inclusion: options)
+        end
+
+        def validates_exclusion_of(*attributes, **options)
+          validates(*attributes, exclusion: options)
+        end
+
+        # Registers a custom validation as either an instance method name
+        # (validate :check_something) or a block run via instance_exec.
+        # Either form is expected to call errors.add itself.
+        def validate(method_name = nil, &block)
+          custom_validators << (method_name || block)
+        end
       end
 
       def errors
@@ -23,7 +46,10 @@ module Prism
 
       def valid?
         errors.clear
+        return false unless run_callbacks(:before_validation)
         self.class.validators.each { |validator| run_validator(validator) }
+        self.class.custom_validators.each { |validator| run_custom_validator(validator) }
+        run_callbacks(:after_validation)
         errors.empty?
       end
 
@@ -39,40 +65,107 @@ module Prism
         when :uniqueness then validate_uniqueness(validator[:attribute], validator[:config])
         when :format then validate_format(validator[:attribute], validator[:config])
         when :length then validate_length(validator[:attribute], validator[:config])
+        when :numericality then validate_numericality(validator[:attribute], validator[:config])
+        when :inclusion then validate_inclusion(validator[:attribute], validator[:config])
+        when :exclusion then validate_exclusion(validator[:attribute], validator[:config])
         else raise ArgumentError, "unknown validator #{validator[:kind]}"
         end
       end
 
+      def run_custom_validator(validator)
+        validator.is_a?(Proc) ? instance_exec(&validator) : send(validator)
+      end
+
       def validate_presence(attribute, config)
         return unless config
-        value = self[attribute]
+        value = public_send(attribute)
         return unless value.nil? || (value.respond_to?(:empty?) && value.empty?)
         errors.add(attribute, message_for(config, 'must be present'))
       end
 
       def validate_uniqueness(attribute, config)
         return unless config
-        value = self[attribute]
+        value = public_send(attribute)
         return if value.nil?
-        conflict = self.class.where(attribute => value).any? { |record| !persisted? || record.id != id }
+        scope = config.is_a?(Hash) ? Array(config[:scope]) : []
+        candidates = scope.inject(self.class.where(attribute => value)) do |relation, scope_attribute|
+          relation.where(scope_attribute => public_send(scope_attribute))
+        end
+        conflict = candidates.any? { |record| !persisted? || record.id != id }
         errors.add(attribute, message_for(config, 'must be unique')) if conflict
       end
 
       def validate_format(attribute, config)
         pattern = config.is_a?(Hash) ? config[:with] : config
         return unless pattern
-        value = self[attribute]
+        value = public_send(attribute)
         return if value.nil?
         return if value.to_s.match?(pattern)
         errors.add(attribute, message_for(config, 'is invalid'))
       end
 
       def validate_length(attribute, config)
-        value = self[attribute].to_s
+        value = public_send(attribute).to_s
         errors.add(attribute, "is too short (minimum #{config[:minimum]})") if config[:minimum] && value.length < config[:minimum]
         errors.add(attribute, "is too long (maximum #{config[:maximum]})") if config[:maximum] && value.length > config[:maximum]
       end
 
+      NUMERICALITY_CHECKS = {
+        greater_than: ->(n, v) { n > v },
+        greater_than_or_equal_to: ->(n, v) { n >= v },
+        less_than: ->(n, v) { n < v },
+        less_than_or_equal_to: ->(n, v) { n <= v },
+        equal_to: ->(n, v) { n == v },
+        other_than: ->(n, v) { n != v }
+      }.freeze
+
+      def validate_numericality(attribute, config)
+        config = config.is_a?(Hash) ? config : {}
+        value = public_send(attribute)
+        return if value.nil? && config[:allow_nil]
+
+        number = coerce_number(value)
+        return errors.add(attribute, message_for(config, 'is not a number')) if number.nil?
+
+        if config[:only_integer] && number != number.to_i
+          return errors.add(attribute, message_for(config, 'must be an integer'))
+        end
+
+        NUMERICALITY_CHECKS.each do |key, check|
+          next unless config.key?(key)
+          next if check.call(number, config[key])
+          errors.add(attribute, message_for(config, "must be #{key.to_s.tr('_', ' ')} #{config[key]}"))
+        end
+
+        errors.add(attribute, message_for(config, 'must be odd')) if config[:odd] && number.to_i.even?
+        errors.add(attribute, message_for(config, 'must be even')) if config[:even] && number.to_i.odd?
+      end
+
+      def coerce_number(value)
+        return value if value.is_a?(Numeric)
+        return nil if value.nil?
+
+        Float(value.to_s)
+      rescue ArgumentError, TypeError
+        nil
+      end
+
+      def validate_inclusion(attribute, config)
+        config = config.is_a?(Hash) ? config : { in: config }
+        value = public_send(attribute)
+        return if value.nil? && config[:allow_nil]
+        set = config[:in] || config[:within]
+        errors.add(attribute, message_for(config, 'is not included in the list')) unless set.include?(value)
+      end
+
+      def validate_exclusion(attribute, config)
+        config = config.is_a?(Hash) ? config : { in: config }
+        value = public_send(attribute)
+        return if value.nil? && config[:allow_nil]
+        set = config[:in] || config[:within]
+        errors.add(attribute, message_for(config, 'is reserved')) if set.include?(value)
+      end
+
       def message_for(config, default)
         config.is_a?(Hash) && config[:message] ? config[:message] : default
       end