diff --git a/activemodel/CHANGELOG.md b/activemodel/CHANGELOG.md
index fb4b972282..175912b240 100644
--- a/activemodel/CHANGELOG.md
+++ b/activemodel/CHANGELOG.md
@@ -1,7 +1,25 @@
+*   Add `ActiveModel::Errors#details`
+
+    To be able to return type of used validator, one can now call `details`
+    on Errors instance:
+
+    ```ruby
+    class User < ActiveRecord::Base
+      validates :name, presence: true
+    end
+    ```
+
+    ```ruby
+    user = User.new; user.valid?; user.errors.details
+    => {name: [{error: :blank}]}
+    ```
+
+    *Wojciech Wnętrzak*
+
 *   Change validates_acceptance_of to accept true by default.
 
     The default for validates_acceptance_of is now "1" and true.
-    In the past, only "1" was the default and you were required to add 
+    In the past, only "1" was the default and you were required to add
     accept: true.
 
 *   Remove deprecated `ActiveModel::Dirty#reset_#{attribute}` and
diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 477edbd120..912448e43c 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -23,7 +23,7 @@ module ActiveModel
   #     attr_reader   :errors
   #
   #     def validate!
-  #       errors.add(:name, "cannot be nil") if name.nil?
+  #       errors.add(:name, :blank, message: "cannot be nil") if name.nil?
   #     end
   #
   #     # The following methods are needed to be minimally implemented
@@ -58,8 +58,9 @@ module ActiveModel
     include Enumerable
 
     CALLBACKS_OPTIONS = [:if, :unless, :on, :allow_nil, :allow_blank, :strict]
+    MESSAGE_OPTIONS = [:message]
 
-    attr_reader :messages
+    attr_reader :messages, :details
 
     # Pass in the instance of the object that is using the errors object.
     #
@@ -71,10 +72,12 @@ module ActiveModel
     def initialize(base)
       @base     = base
       @messages = {}
+      @details  = Hash.new { |details, attribute| details[attribute] = [] }
     end
 
     def initialize_dup(other) # :nodoc:
       @messages = other.messages.dup
+      @details  = other.details.dup
       super
     end
 
@@ -85,6 +88,7 @@ module ActiveModel
     #   person.errors.full_messages # => []
     def clear
       messages.clear
+      details.clear
     end
 
     # Returns +true+ if the error messages include an error for the given key
@@ -126,6 +130,7 @@ module ActiveModel
     #   person.errors.get(:name)    # => nil
     def delete(key)
       messages.delete(key)
+      details.delete(key)
     end
 
     # When passed a symbol or a name of a method, returns an array of errors
@@ -149,12 +154,12 @@ module ActiveModel
     # Yields the attribute and the error for that attribute. If the attribute
     # has more than one error message, yields once for each error message.
     #
-    #   person.errors.add(:name, "can't be blank")
+    #   person.errors.add(:name, :blank, message: "can't be blank")
     #   person.errors.each do |attribute, error|
     #     # Will yield :name and "can't be blank"
     #   end
     #
-    #   person.errors.add(:name, "must be specified")
+    #   person.errors.add(:name, :not_specified, message: "must be specified")
     #   person.errors.each do |attribute, error|
     #     # Will yield :name and "can't be blank"
     #     # then yield :name and "must be specified"
@@ -167,9 +172,9 @@ module ActiveModel
 
     # Returns the number of error messages.
     #
-    #   person.errors.add(:name, "can't be blank")
+    #   person.errors.add(:name, :blank, message: "can't be blank")
     #   person.errors.size # => 1
-    #   person.errors.add(:name, "must be specified")
+    #   person.errors.add(:name, :not_specified, message: "must be specified")
     #   person.errors.size # => 2
     def size
       values.flatten.size
@@ -193,8 +198,8 @@ module ActiveModel
 
     # Returns an array of error messages, with the attribute name included.
     #
-    #   person.errors.add(:name, "can't be blank")
-    #   person.errors.add(:name, "must be specified")
+    #   person.errors.add(:name, :blank, message: "can't be blank")
+    #   person.errors.add(:name, :not_specified, message: "must be specified")
     #   person.errors.to_a # => ["name can't be blank", "name must be specified"]
     def to_a
       full_messages
@@ -202,9 +207,9 @@ module ActiveModel
 
     # Returns the number of error messages.
     #
-    #   person.errors.add(:name, "can't be blank")
+    #   person.errors.add(:name, :blank, message: "can't be blank")
     #   person.errors.count # => 1
-    #   person.errors.add(:name, "must be specified")
+    #   person.errors.add(:name, :not_specified, message: "must be specified")
     #   person.errors.count # => 2
     def count
       to_a.size
@@ -223,8 +228,8 @@ module ActiveModel
 
     # Returns an xml formatted representation of the Errors hash.
     #
-    #   person.errors.add(:name, "can't be blank")
-    #   person.errors.add(:name, "must be specified")
+    #   person.errors.add(:name, :blank, message: "can't be blank")
+    #   person.errors.add(:name, :not_specified, message: "must be specified")
     #   person.errors.to_xml
     #   # =>
     #   #  <?xml version=\"1.0\" encoding=\"UTF-8\"?>
@@ -261,17 +266,20 @@ module ActiveModel
       end
     end
 
-    # Adds +message+ to the error messages on +attribute+. More than one error
-    # can be added to the same +attribute+. If no +message+ is supplied,
-    # <tt>:invalid</tt> is assumed.
+    # Adds +message+ to the error messages and used validator type to +details+ on +attribute+.
+    # More than one error can be added to the same +attribute+.
+    # If no +message+ is supplied, <tt>:invalid</tt> is assumed.
     #
     #   person.errors.add(:name)
     #   # => ["is invalid"]
-    #   person.errors.add(:name, 'must be implemented')
+    #   person.errors.add(:name, :not_implemented, message: "must be implemented")
     #   # => ["is invalid", "must be implemented"]
     #
     #   person.errors.messages
-    #   # => {:name=>["must be implemented", "is invalid"]}
+    #   # => {:name=>["is invalid", "must be implemented"]}
+    #
+    #   person.errors.details
+    #   # => {:name=>[{error: :not_implemented}, {error: :invalid}]}
     #
     # If +message+ is a symbol, it will be translated using the appropriate
     # scope (see +generate_message+).
@@ -293,16 +301,22 @@ module ActiveModel
     # +attribute+ should be set to <tt>:base</tt> if the error is not
     # directly associated with a single attribute.
     #
-    #   person.errors.add(:base, "either name or email must be present")
+    #   person.errors.add(:base, :name_or_email_blank,
+    #     message: "either name or email must be present")
     #   person.errors.messages
     #   # => {:base=>["either name or email must be present"]}
+    #   person.errors.details
+    #   # => {:base=>[{error: :name_or_email_blank}]}
     def add(attribute, message = :invalid, options = {})
+      message = message.call if message.respond_to?(:call)
+      detail  = normalize_detail(attribute, message, options)
       message = normalize_message(attribute, message, options)
       if exception = options[:strict]
         exception = ActiveModel::StrictValidationFailed if exception == true
         raise exception, full_message(attribute, message)
       end
 
+      details[attribute.to_sym] << detail
       self[attribute] << message
     end
 
@@ -339,6 +353,7 @@ module ActiveModel
     #   person.errors.add :name, :blank
     #   person.errors.added? :name, :blank # => true
     def added?(attribute, message = :invalid, options = {})
+      message = message.call if message.respond_to?(:call)
       message = normalize_message(attribute, message, options)
       self[attribute].include? message
     end
@@ -447,12 +462,14 @@ module ActiveModel
       case message
       when Symbol
         generate_message(attribute, message, options.except(*CALLBACKS_OPTIONS))
-      when Proc
-        message.call
       else
         message
       end
     end
+
+    def normalize_detail(attribute, message, options)
+      { error: message }.merge(options.except(*CALLBACKS_OPTIONS + MESSAGE_OPTIONS))
+    end
   end
 
   # Raised when a validation cannot be corrected by end users and are considered
diff --git a/activemodel/test/cases/errors_test.rb b/activemodel/test/cases/errors_test.rb
index efedd9055f..9cfba9812b 100644
--- a/activemodel/test/cases/errors_test.rb
+++ b/activemodel/test/cases/errors_test.rb
@@ -323,4 +323,46 @@ class ErrorsTest < ActiveModel::TestCase
     person.errors.expects(:generate_message).with(:name, :blank, { message: 'custom' })
     person.errors.add_on_blank :name, message: 'custom'
   end
+
+  test "details returns added error detail" do
+    person = Person.new
+    person.errors.add(:name, :invalid)
+    assert_equal({ name: [{ error: :invalid }] }, person.errors.details)
+  end
+
+  test "details returns added error detail with custom option" do
+    person = Person.new
+    person.errors.add(:name, :greater_than, count: 5)
+    assert_equal({ name: [{ error: :greater_than, count: 5 }] }, person.errors.details)
+  end
+
+  test "details do not include message option" do
+    person = Person.new
+    person.errors.add(:name, :invalid, message: "is bad")
+    assert_equal({ name: [{ error: :invalid }] }, person.errors.details)
+  end
+
+  test "dup duplicates details" do
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:name, :invalid)
+    errors_dup = errors.dup
+    errors_dup.add(:name, :taken)
+    assert_not_same errors_dup.details, errors.details
+  end
+
+  test "delete removes details on given attribute" do
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:name, :invalid)
+    errors.delete(:name)
+    assert_empty errors.details[:name]
+  end
+
+  test "clear removes details" do
+    person = Person.new
+    person.errors.add(:name, :invalid)
+
+    assert_equal 1, person.errors.details.count
+    person.errors.clear
+    assert person.errors.details.empty?
+  end
 end
diff --git a/guides/source/active_record_validations.md b/guides/source/active_record_validations.md
index c9af70934a..84925072f2 100644
--- a/guides/source/active_record_validations.md
+++ b/guides/source/active_record_validations.md
@@ -227,8 +227,26 @@ end
 ```
 
 We'll cover validation errors in greater depth in the [Working with Validation
-Errors](#working-with-validation-errors) section. For now, let's turn to the
-built-in validation helpers that Rails provides by default.
+Errors](#working-with-validation-errors) section.
+
+### `errors.details`
+
+To check what validator type was used on invalid attribute, you can use
+`errors.details[:attribute]`. It returns array of hashes where under `:error`
+ key you will find symbol of used validator.
+
+```ruby
+class Person < ActiveRecord::Base
+  validates :name, presence: true
+end
+
+>> person = Person.new
+>> person.valid?
+>> person.errors.details[:name] #=> [{error: :blank}]
+```
+
+Using `details` with custom validators are covered in the [Working with
+Validation Errors](#working-with-validation-errors) section.
 
 Validation Helpers
 ------------------
@@ -1074,6 +1092,42 @@ Another way to do this is using `[]=` setter
    # => ["Name cannot contain the characters !@#%*()_-+="]
 ```
 
+### `errors.details`
+
+You can add validator type to details hash when using `errors.add` method.
+
+```ruby
+  class Person < ActiveRecord::Base
+    def a_method_used_for_validation_purposes
+      errors.add(:name, :invalid_characters)
+    end
+  end
+
+  person = Person.create(name: "!@#")
+
+  person.errors.details[:name]
+   # => [{error: :invalid_characters}]
+```
+
+To improve error details to contain not allowed characters set, you can
+pass additional options to `errors.add` method.
+
+```ruby
+  class Person < ActiveRecord::Base
+    def a_method_used_for_validation_purposes
+      errors.add(:name, :invalid_characters, not_allowed: "!@#%*()_-+=")
+    end
+  end
+
+  person = Person.create(name: "!@#")
+
+  person.errors.details[:name]
+  # => [{error: :invalid_characters, not_allowed: "!@#%*()_-+="}]
+```
+
+All built in Rails validators populate details hash with corresponding
+validator types.
+
 ### `errors[:base]`
 
 You can add error messages that are related to the object's state as a whole, instead of being related to a specific attribute. You can use this method when you want to say that the object is invalid, no matter the values of its attributes. Since `errors[:base]` is an array, you can simply add a string to it and it will be used as an error message.