diff --git a/.rubocop.yml b/.rubocop.yml
index 41e236ee..a31e42f0 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -59,7 +59,7 @@ Style/MethodCalledOnDoEndBlock:
   Enabled: false
 
 Naming/VariableNumber:
-  Enabled: false
+  EnforcedColonStyle: normalcase
 
 Style/StringLiterals:
   ConsistentQuotesInMultiline: true
diff --git a/lib/graphql_devise.rb b/lib/graphql_devise.rb
index 5d789d29..3ec8627e 100644
--- a/lib/graphql_devise.rb
+++ b/lib/graphql_devise.rb
@@ -2,21 +2,19 @@
 require 'graphql'
 require 'devise_token_auth'
 
+module GraphqlDevise
+  class Error < StandardError; end
+
+  class InvalidMountOptionsError < GraphqlDevise::Error; end
+end
+
 require 'graphql_devise/concerns/controller_methods'
 require 'graphql_devise/types/authenticatable_type'
 require 'graphql_devise/types/credential_type'
 require 'graphql_devise/types/mutation_type'
 require 'graphql_devise/types/query_type'
-require 'graphql_devise/mutations/base'
-require 'graphql_devise/mutations/login'
-require 'graphql_devise/mutations/logout'
-require 'graphql_devise/mutations/resend_confirmation'
-require 'graphql_devise/mutations/send_password_reset'
-require 'graphql_devise/mutations/sign_up'
-require 'graphql_devise/mutations/update_password'
-require 'graphql_devise/resolvers/base'
-require 'graphql_devise/resolvers/check_password_token'
-require 'graphql_devise/resolvers/confirm_account'
+require 'graphql_devise/default_operations/mutations'
+require 'graphql_devise/default_operations/resolvers'
 require 'graphql_devise/resolvers/dummy'
 
 require 'graphql_devise/engine'
@@ -24,11 +22,8 @@
 require 'graphql_devise/error_codes'
 require 'graphql_devise/user_error'
 require 'graphql_devise/detailed_user_error'
-require 'graphql_devise/rails/queries_preparer'
-require 'graphql_devise/rails/mutations_preparer'
-require 'graphql_devise/rails/operation_checker'
-require 'graphql_devise/rails/operation_sanitizer'
 
-module GraphqlDevise
-  class Error < StandardError; end
-end
+require 'graphql_devise/mount_method/options_validator'
+require 'graphql_devise/mount_method/queries_preparer'
+require 'graphql_devise/mount_method/mutations_preparer'
+require 'graphql_devise/mount_method/operation_sanitizer'
diff --git a/lib/graphql_devise/default_operations/mutations.rb b/lib/graphql_devise/default_operations/mutations.rb
new file mode 100644
index 00000000..2b9f76f0
--- /dev/null
+++ b/lib/graphql_devise/default_operations/mutations.rb
@@ -0,0 +1,20 @@
+require 'graphql_devise/mutations/base'
+require 'graphql_devise/mutations/login'
+require 'graphql_devise/mutations/logout'
+require 'graphql_devise/mutations/resend_confirmation'
+require 'graphql_devise/mutations/send_password_reset'
+require 'graphql_devise/mutations/sign_up'
+require 'graphql_devise/mutations/update_password'
+
+module GraphqlDevise
+  module DefaultOperations
+    MUTATIONS = {
+      login:               GraphqlDevise::Mutations::Login,
+      logout:              GraphqlDevise::Mutations::Logout,
+      sign_up:             GraphqlDevise::Mutations::SignUp,
+      update_password:     GraphqlDevise::Mutations::UpdatePassword,
+      send_password_reset: GraphqlDevise::Mutations::SendPasswordReset,
+      resend_confirmation: GraphqlDevise::Mutations::ResendConfirmation
+    }.freeze
+  end
+end
diff --git a/lib/graphql_devise/default_operations/resolvers.rb b/lib/graphql_devise/default_operations/resolvers.rb
new file mode 100644
index 00000000..a1be31b9
--- /dev/null
+++ b/lib/graphql_devise/default_operations/resolvers.rb
@@ -0,0 +1,12 @@
+require 'graphql_devise/resolvers/base'
+require 'graphql_devise/resolvers/check_password_token'
+require 'graphql_devise/resolvers/confirm_account'
+
+module GraphqlDevise
+  module DefaultOperations
+    QUERIES = {
+      confirm_account:      GraphqlDevise::Resolvers::ConfirmAccount,
+      check_password_token: GraphqlDevise::Resolvers::CheckPasswordToken
+    }.freeze
+  end
+end
diff --git a/lib/graphql_devise/mount_method/mutations_preparer.rb b/lib/graphql_devise/mount_method/mutations_preparer.rb
new file mode 100644
index 00000000..64a467e3
--- /dev/null
+++ b/lib/graphql_devise/mount_method/mutations_preparer.rb
@@ -0,0 +1,27 @@
+module GraphqlDevise
+  module MountMethod
+    class MutationsPreparer
+      def self.call(resource:, mutations:, authenticatable_type:)
+        new(resource: resource, mutations: mutations, authenticatable_type: authenticatable_type).call
+      end
+
+      def initialize(resource:, mutations:, authenticatable_type:)
+        @mapping_name         = resource.underscore.tr('/', '_').to_sym
+        @mutations            = mutations
+        @authenticatable_type = authenticatable_type
+      end
+
+      def call
+        @mutations.each_with_object({}) do |(action, mutation), result|
+          mapped_action = "#{@mapping_name}_#{action}".to_sym
+          new_mutation  = Class.new(mutation)
+          new_mutation.graphql_name(mapped_action.to_s.camelize(:upper))
+          new_mutation.field(:authenticatable, @authenticatable_type, null: true)
+          new_mutation.instance_variable_set(:@resource_name, @mapping_name)
+
+          result[mapped_action] = new_mutation
+        end
+      end
+    end
+  end
+end
diff --git a/lib/graphql_devise/mount_method/operation_sanitizer.rb b/lib/graphql_devise/mount_method/operation_sanitizer.rb
new file mode 100644
index 00000000..50a4578a
--- /dev/null
+++ b/lib/graphql_devise/mount_method/operation_sanitizer.rb
@@ -0,0 +1,35 @@
+module GraphqlDevise
+  module MountMethod
+    class OperationSanitizer
+      def self.call(default:, custom:, only:, skipped:)
+        new(
+          default: default,
+          custom:  custom,
+          only:    only,
+          skipped: skipped
+        ).call
+      end
+
+      def initialize(default:, custom:, only:, skipped:)
+        @default = default
+        @custom  = custom
+        @only    = only
+        @skipped = skipped
+      end
+
+      def call
+        result = @default.merge(@custom.slice(*operations_whitelist))
+        result = result.slice(*@only) if @only.present?
+        result = result.except(*@skipped) if @skipped.present?
+
+        result
+      end
+
+      private
+
+      def operations_whitelist
+        @default.keys
+      end
+    end
+  end
+end
diff --git a/lib/graphql_devise/mount_method/option_validators/provided_operations_validator.rb b/lib/graphql_devise/mount_method/option_validators/provided_operations_validator.rb
new file mode 100644
index 00000000..f5ed7a17
--- /dev/null
+++ b/lib/graphql_devise/mount_method/option_validators/provided_operations_validator.rb
@@ -0,0 +1,44 @@
+require_relative 'supported_operations_validator'
+
+module GraphqlDevise
+  module MountMethod
+    module OptionValidators
+      class ProvidedOperationsValidator
+        def initialize(options: {}, supported_operations: {})
+          @options              = options || {}
+          @supported_operations = supported_operations
+        end
+
+        def validate!
+          skipped        = @options.fetch(:skip, [])
+          only           = @options.fetch(:only, [])
+          operations     = @options.fetch(:operations, {})
+          supported_keys = @supported_operations.keys
+
+          raise_on_invalid_option_type!(:skip, skipped, Array)
+          raise_on_invalid_option_type!(:only, only, Array)
+          raise_on_invalid_option_type!(:operations, operations, Hash)
+
+          custom = operations.keys
+
+          [
+            SupportedOperationsValidator.new(provided_operations: skipped, key: :skip, supported_operations: supported_keys),
+            SupportedOperationsValidator.new(provided_operations: only, key: :only, supported_operations: supported_keys),
+            SupportedOperationsValidator.new(provided_operations: custom, key: :operations, supported_operations: supported_keys)
+          ].each(&:validate!)
+        end
+
+        private
+
+        def raise_on_invalid_option_type!(key, value, expected_class)
+          unless value.is_a?(expected_class)
+            raise(
+              GraphqlDevise::InvalidMountOptionsError,
+              "#{key} option contains value of invalid value. Value must be #{expected_class.name}."
+            )
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/graphql_devise/mount_method/option_validators/skip_only_validator.rb b/lib/graphql_devise/mount_method/option_validators/skip_only_validator.rb
new file mode 100644
index 00000000..d14ea306
--- /dev/null
+++ b/lib/graphql_devise/mount_method/option_validators/skip_only_validator.rb
@@ -0,0 +1,20 @@
+module GraphqlDevise
+  module MountMethod
+    module OptionValidators
+      class SkipOnlyValidator
+        def initialize(options: {})
+          @options = options || {}
+        end
+
+        def validate!
+          if [@options[:skip], @options[:only]].all?(&:present?)
+            raise(
+              GraphqlDevise::InvalidMountOptionsError,
+              "Can't specify both `skip` and `only` options when mounting the route."
+            )
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/graphql_devise/mount_method/option_validators/supported_operations_validator.rb b/lib/graphql_devise/mount_method/option_validators/supported_operations_validator.rb
new file mode 100644
index 00000000..6c54d748
--- /dev/null
+++ b/lib/graphql_devise/mount_method/option_validators/supported_operations_validator.rb
@@ -0,0 +1,24 @@
+module GraphqlDevise
+  module MountMethod
+    module OptionValidators
+      class SupportedOperationsValidator
+        def initialize(provided_operations: [], supported_operations: [], key:)
+          @provided_operations  = provided_operations
+          @supported_operations = supported_operations
+          @key                  = key
+        end
+
+        def validate!
+          unsupported_operations = @provided_operations - @supported_operations
+
+          if unsupported_operations.present?
+            raise(
+              GraphqlDevise::InvalidMountOptionsError,
+              "#{@key} option contains unsupported operations: \"#{unsupported_operations.join(', ')}\". Check for typos."
+            )
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/graphql_devise/mount_method/options_validator.rb b/lib/graphql_devise/mount_method/options_validator.rb
new file mode 100644
index 00000000..2c0f295d
--- /dev/null
+++ b/lib/graphql_devise/mount_method/options_validator.rb
@@ -0,0 +1,16 @@
+require_relative 'option_validators/skip_only_validator'
+require_relative 'option_validators/provided_operations_validator'
+
+module GraphqlDevise
+  module MountMethod
+    class OptionsValidator
+      def initialize(validators = [])
+        @validators = validators
+      end
+
+      def validate!
+        @validators.each(&:validate!)
+      end
+    end
+  end
+end
diff --git a/lib/graphql_devise/mount_method/queries_preparer.rb b/lib/graphql_devise/mount_method/queries_preparer.rb
new file mode 100644
index 00000000..f6614774
--- /dev/null
+++ b/lib/graphql_devise/mount_method/queries_preparer.rb
@@ -0,0 +1,27 @@
+module GraphqlDevise
+  module MountMethod
+    class QueriesPreparer
+      def self.call(resource:, queries:, authenticatable_type:)
+        new(resource: resource, queries: queries, authenticatable_type: authenticatable_type).call
+      end
+
+      def initialize(resource:, queries:, authenticatable_type:)
+        @mapping_name         = resource.underscore.tr('/', '_').to_sym
+        @queries              = queries
+        @authenticatable_type = authenticatable_type
+      end
+
+      def call
+        @queries.each_with_object({}) do |(action, query), result|
+          mapped_action = "#{@mapping_name}_#{action}".to_sym
+          new_query     = Class.new(query)
+          new_query.graphql_name(mapped_action.to_s.camelize(:upper))
+          new_query.type(@authenticatable_type, null: true)
+          new_query.instance_variable_set(:@resource_name, @mapping_name)
+
+          result[mapped_action] = new_query
+        end
+      end
+    end
+  end
+end
diff --git a/lib/graphql_devise/rails/mutations_preparer.rb b/lib/graphql_devise/rails/mutations_preparer.rb
deleted file mode 100644
index d5fe0cbf..00000000
--- a/lib/graphql_devise/rails/mutations_preparer.rb
+++ /dev/null
@@ -1,34 +0,0 @@
-module GraphqlDevise
-  class MutationsPreparer
-    DEFAULT_MUTATIONS = {
-      login:               GraphqlDevise::Mutations::Login,
-      logout:              GraphqlDevise::Mutations::Logout,
-      sign_up:             GraphqlDevise::Mutations::SignUp,
-      update_password:     GraphqlDevise::Mutations::UpdatePassword,
-      send_password_reset: GraphqlDevise::Mutations::SendPasswordReset,
-      resend_confirmation: GraphqlDevise::Mutations::ResendConfirmation
-    }.freeze
-
-    def self.call(resource:, mutations:, authenticatable_type:)
-      new(resource: resource, mutations: mutations, authenticatable_type: authenticatable_type).call
-    end
-
-    def initialize(resource:, mutations:, authenticatable_type:)
-      @mapping_name         = resource.underscore.tr('/', '_').to_sym
-      @mutations            = mutations
-      @authenticatable_type = authenticatable_type
-    end
-
-    def call
-      @mutations.each_with_object({}) do |(action, mutation), result|
-        mapped_action = "#{@mapping_name}_#{action}".to_sym
-        new_mutation  = Class.new(mutation)
-        new_mutation.graphql_name(mapped_action.to_s.camelize(:upper))
-        new_mutation.field(:authenticatable, @authenticatable_type, null: true)
-        new_mutation.instance_variable_set(:@resource_name, @mapping_name)
-
-        result[mapped_action] = new_mutation
-      end
-    end
-  end
-end
diff --git a/lib/graphql_devise/rails/operation_checker.rb b/lib/graphql_devise/rails/operation_checker.rb
deleted file mode 100644
index e22872a1..00000000
--- a/lib/graphql_devise/rails/operation_checker.rb
+++ /dev/null
@@ -1,59 +0,0 @@
-module GraphqlDevise
-  class OperationChecker
-    def self.call(mutations:, queries:, custom:, only:, skipped:)
-      new(
-        mutations: mutations,
-        queries:   queries,
-        custom:    custom,
-        only:      only,
-        skipped:   skipped
-      ).call
-    end
-
-    def initialize(mutations:, queries:, custom:, only:, skipped:)
-      @mutations = mutations
-      @queries   = queries
-      @custom    = custom
-      @only      = only
-      @skipped   = skipped
-    end
-
-    def call
-      supported_operations = @mutations.keys + @queries.keys
-
-      if [@skipped, @only].all?(&:any?)
-        raise(
-          GraphqlDevise::Error,
-          "Can't specify both `skip` and `only` options when mounting the route."
-        )
-      end
-
-      @custom.keys.each do |custom_op|
-        next if supported_operations.include?(custom_op)
-
-        raise(
-          GraphqlDevise::Error,
-          "Custom operation \"#{custom_op}\" is not supported. Check for typos."
-        )
-      end
-
-      @skipped.each do |skipped_op|
-        next if supported_operations.include?(skipped_op)
-
-        raise(
-          GraphqlDevise::Error,
-          "Trying to skip unsupported operation \"#{skipped_op}\". Check for typos."
-        )
-      end
-
-      @only.each do |only_op|
-        next if supported_operations.include?(only_op)
-
-        raise(
-          GraphqlDevise::Error,
-          "The \"only\" operation \"#{only_op}\" is not supported. Check for typos."
-        )
-      end
-    end
-  end
-end
diff --git a/lib/graphql_devise/rails/operation_sanitizer.rb b/lib/graphql_devise/rails/operation_sanitizer.rb
deleted file mode 100644
index 1fb8922e..00000000
--- a/lib/graphql_devise/rails/operation_sanitizer.rb
+++ /dev/null
@@ -1,33 +0,0 @@
-module GraphqlDevise
-  class OperationSanitizer
-    def self.call(default:, custom:, only:, skipped:)
-      new(
-        default: default,
-        custom:  custom,
-        only:    only,
-        skipped: skipped
-      ).call
-    end
-
-    def initialize(default:, custom:, only:, skipped:)
-      @default = default
-      @custom  = custom
-      @only    = only
-      @skipped = skipped
-    end
-
-    def call
-      result = @default.merge(@custom.slice(*operations_whitelist))
-      result = result.slice(*@only) if @only.present?
-      result = result.except(*@skipped) if @skipped.present?
-
-      result
-    end
-
-    private
-
-    def operations_whitelist
-      @default.keys
-    end
-  end
-end
diff --git a/lib/graphql_devise/rails/queries_preparer.rb b/lib/graphql_devise/rails/queries_preparer.rb
deleted file mode 100644
index f20705ea..00000000
--- a/lib/graphql_devise/rails/queries_preparer.rb
+++ /dev/null
@@ -1,30 +0,0 @@
-module GraphqlDevise
-  class QueriesPreparer
-    DEFAULT_QUERIES = {
-      confirm_account:      GraphqlDevise::Resolvers::ConfirmAccount,
-      check_password_token: GraphqlDevise::Resolvers::CheckPasswordToken
-    }.freeze
-
-    def self.call(resource:, queries:, authenticatable_type:)
-      new(resource: resource, queries: queries, authenticatable_type: authenticatable_type).call
-    end
-
-    def initialize(resource:, queries:, authenticatable_type:)
-      @mapping_name         = resource.underscore.tr('/', '_').to_sym
-      @queries              = queries
-      @authenticatable_type = authenticatable_type
-    end
-
-    def call
-      @queries.each_with_object({}) do |(action, query), result|
-        mapped_action = "#{@mapping_name}_#{action}".to_sym
-        new_query     = Class.new(query)
-        new_query.graphql_name(mapped_action.to_s.camelize(:upper))
-        new_query.type(@authenticatable_type, null: true)
-        new_query.instance_variable_set(:@resource_name, @mapping_name)
-
-        result[mapped_action] = new_query
-      end
-    end
-  end
-end
diff --git a/lib/graphql_devise/rails/routes.rb b/lib/graphql_devise/rails/routes.rb
index 01b30286..1536f511 100644
--- a/lib/graphql_devise/rails/routes.rb
+++ b/lib/graphql_devise/rails/routes.rb
@@ -10,29 +10,35 @@ class Mapper
       :invitations
     ].freeze
 
-    def mount_graphql_devise_for(resource, opts = {})
-      custom_operations    = opts.fetch(:operations, {})
-      skipped_operations   = opts.fetch(:skip, [])
-      only_operations      = opts.fetch(:only, [])
-      additional_mutations = opts.fetch(:additional_mutations, {})
-      additional_queries   = opts.fetch(:additional_queries, {})
-      path                 = opts.fetch(:at, '/graphql_auth')
+    def mount_graphql_devise_for(resource, options = {})
+      default_operations = GraphqlDevise::DefaultOperations::MUTATIONS.merge(GraphqlDevise::DefaultOperations::QUERIES)
+
+      GraphqlDevise::MountMethod::OptionsValidator.new(
+        [
+          GraphqlDevise::MountMethod::OptionValidators::SkipOnlyValidator.new(options: options),
+          GraphqlDevise::MountMethod::OptionValidators::ProvidedOperationsValidator.new(
+            options: options, supported_operations: default_operations
+          )
+        ]
+      ).validate!
+
+      custom_operations    = options.fetch(:operations, {})
+      skipped_operations   = options.fetch(:skip, [])
+      only_operations      = options.fetch(:only, [])
+      additional_mutations = options.fetch(:additional_mutations, {})
+      additional_queries   = options.fetch(:additional_queries, {})
+      path                 = options.fetch(:at, '/graphql_auth')
       mapping_name         = resource.underscore.tr('/', '_').to_sym
-      authenticatable_type = opts[:authenticatable_type].presence ||
-        "Types::#{resource}Type".safe_constantize ||
-        GraphqlDevise::Types::AuthenticatableType
-      param_operations     = {
+      authenticatable_type = options[:authenticatable_type].presence ||
+                             "Types::#{resource}Type".safe_constantize ||
+                             GraphqlDevise::Types::AuthenticatableType
+
+      param_operations = {
         custom:  custom_operations,
         only:    only_operations,
         skipped: skipped_operations
       }
 
-      GraphqlDevise::OperationChecker.call(
-        mutations: GraphqlDevise::MutationsPreparer::DEFAULT_MUTATIONS,
-        queries:   GraphqlDevise::QueriesPreparer::DEFAULT_QUERIES,
-        **param_operations
-      )
-
       devise_for(
         resource.pluralize.underscore.tr('/', '_').to_sym,
         module:     :devise,
@@ -40,18 +46,18 @@ def mount_graphql_devise_for(resource, opts = {})
         skip:       DEVISE_OPERATIONS
       )
 
-      prepared_mutations = GraphqlDevise::MutationsPreparer.call(
+      prepared_mutations = GraphqlDevise::MountMethod::MutationsPreparer.call(
         resource:             resource,
-        mutations:            GraphqlDevise::OperationSanitizer.call(
-          default: GraphqlDevise::MutationsPreparer::DEFAULT_MUTATIONS, **param_operations
+        mutations:            GraphqlDevise::MountMethod::OperationSanitizer.call(
+          default: GraphqlDevise::DefaultOperations::MUTATIONS, **param_operations
         ),
         authenticatable_type: authenticatable_type
       )
 
-      prepared_queries = GraphqlDevise::QueriesPreparer.call(
+      prepared_queries = GraphqlDevise::MountMethod::QueriesPreparer.call(
         resource:             resource,
-        queries:              GraphqlDevise::OperationSanitizer.call(
-          default: GraphqlDevise::QueriesPreparer::DEFAULT_QUERIES, **param_operations
+        queries:              GraphqlDevise::MountMethod::OperationSanitizer.call(
+          default: GraphqlDevise::DefaultOperations::QUERIES, **param_operations
         ),
         authenticatable_type: authenticatable_type
       )
@@ -61,7 +67,7 @@ def mount_graphql_devise_for(resource, opts = {})
       end
 
       if (prepared_mutations.present? || additional_mutations.present?) &&
-          (Gem::Version.new(GraphQL::VERSION) <= Gem::Version.new('1.10.0') || GraphqlDevise::Schema.mutation.nil?)
+         (Gem::Version.new(GraphQL::VERSION) <= Gem::Version.new('1.10.0') || GraphqlDevise::Schema.mutation.nil?)
         GraphqlDevise::Schema.mutation(GraphqlDevise::Types::MutationType)
       end
 
diff --git a/spec/operation_checker_spec.rb b/spec/operation_checker_spec.rb
deleted file mode 100644
index b885e441..00000000
--- a/spec/operation_checker_spec.rb
+++ /dev/null
@@ -1,98 +0,0 @@
-require 'rails_helper'
-
-RSpec.describe GraphqlDevise::OperationChecker do
-  describe '.call' do
-    subject(:result) do
-      -> {
-        described_class.call(
-          mutations: mutations,
-          queries:   queries,
-          custom:    custom,
-          only:      only,
-          skipped:   skipped
-        )
-      }
-    end
-
-    let(:mutations) { { mutation1: Class.new, mutation2: Class.new } }
-    let(:queries)   { { query1: Class.new, query2: Class.new } }
-    let(:custom)    { {} }
-    let(:only)      { [] }
-    let(:skipped)   { [] }
-
-    context 'when there are not custom, only nor skipped operations' do
-      it { is_expected.not_to raise_error }
-    end
-
-    context 'when custom mutations and queries passed are among the defaults' do
-      let(:custom) { { mutation1: Class.new, query2: Class.new } }
-
-      it { is_expected.not_to raise_error }
-    end
-
-    context 'when only operations are among the defaults' do
-      let(:only) { [:mutation1, :query2] }
-
-      it { is_expected.not_to raise_error }
-    end
-
-    context 'when skipped operations are among the defaults' do
-      let(:skipped) { [:mutation2, :query1] }
-
-      it { is_expected.not_to raise_error }
-    end
-
-    context 'when only and skipped operations are both defined' do
-      let(:only)    { [:mutation1, :query2] }
-      let(:skipped) { [:mutation2, :query1] }
-
-      it {
-        is_expected.to(
-          raise_error(
-            GraphqlDevise::Error,
-            "Can't specify both `skip` and `only` options when mounting the route."
-          )
-        )
-      }
-    end
-
-    context 'when custom operations include a not supported item' do
-      let(:custom) { { mutation3: Class.new, query2: Class.new } }
-
-      it {
-        is_expected.to(
-          raise_error(
-            GraphqlDevise::Error,
-            'Custom operation "mutation3" is not supported. Check for typos.'
-          )
-        )
-      }
-    end
-
-    context 'when skipped operations include a not supported item' do
-      let(:skipped) { [:mutation3, :query2] }
-
-      it {
-        is_expected.to(
-          raise_error(
-            GraphqlDevise::Error,
-            'Trying to skip unsupported operation "mutation3". Check for typos.'
-          )
-        )
-      }
-    end
-
-    context 'when only operations include a not supported item' do
-      let(:only) { [:mutation3, :query2] }
-
-      it {
-        is_expected.to(
-          raise_error(
-            GraphqlDevise::Error,
-            'The "only" operation "mutation3" is not supported. Check for typos.'
-          )
-        )
-      }
-    end
-  end
-end
diff --git a/spec/mutations_preparer_spec.rb b/spec/services/mount_method/mutations_preparer_spec.rb
similarity index 94%
rename from spec/mutations_preparer_spec.rb
rename to spec/services/mount_method/mutations_preparer_spec.rb
index 34d24f12..a2c9e3e7 100644
--- a/spec/mutations_preparer_spec.rb
+++ b/spec/services/mount_method/mutations_preparer_spec.rb
@@ -1,6 +1,6 @@
 require 'rails_helper'
 
-RSpec.describe GraphqlDevise::MutationsPreparer do
+RSpec.describe GraphqlDevise::MountMethod::MutationsPreparer do
   describe '.call' do
     subject do
       described_class.call(
diff --git a/spec/operation_sanitizer_spec.rb b/spec/services/mount_method/operation_sanitizer_spec.rb
similarity index 94%
rename from spec/operation_sanitizer_spec.rb
rename to spec/services/mount_method/operation_sanitizer_spec.rb
index 0ecfd99e..a3a20bc8 100644
--- a/spec/operation_sanitizer_spec.rb
+++ b/spec/services/mount_method/operation_sanitizer_spec.rb
@@ -1,6 +1,6 @@
 require 'rails_helper'
 
-RSpec.describe GraphqlDevise::OperationSanitizer do
+RSpec.describe GraphqlDevise::MountMethod::OperationSanitizer do
   describe '.call' do
     subject { described_class.call(default: default, custom: custom, only: only, skipped: skipped) }
 
diff --git a/spec/services/mount_method/option_validators/provided_operations_validator_spec.rb b/spec/services/mount_method/option_validators/provided_operations_validator_spec.rb
new file mode 100644
index 00000000..35de00d0
--- /dev/null
+++ b/spec/services/mount_method/option_validators/provided_operations_validator_spec.rb
@@ -0,0 +1,75 @@
+require 'spec_helper'
+
+RSpec.describe GraphqlDevise::MountMethod::OptionValidators::ProvidedOperationsValidator do
+  describe '#validate!' do
+    subject { -> { described_class.new(options: provided_operations, supported_operations: supported_operations).validate! } }
+
+    let(:supported_operations) { { operation1: 'irrelevant', operation2: 'irrelevant', operation3: 'irrelevant' } }
+
+    context 'when skip option is provided' do
+      let(:provided_operations) { { skip: skipped } }
+
+      context 'when all skipped are supported' do
+        let(:skipped) { [:operation2, :operation3] }
+
+        it { is_expected.not_to raise_error }
+      end
+
+      context 'when skipped contains unsupported operations' do
+        let(:skipped) { [:operation2, :operation3, :invalid] }
+
+        it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, 'skip option contains unsupported operations: "invalid". Check for typos.') }
+      end
+
+      context 'when provided skip value is not an array' do
+        let(:skipped) { 'Invalid value' }
+
+        it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, 'skip option contains value of invalid value. Value must be Array.') }
+      end
+    end
+
+    context 'when only option is provided' do
+      let(:provided_operations) { { only: only } }
+
+      context 'when all only are supported' do
+        let(:only) { [:operation2, :operation3] }
+
+        it { is_expected.not_to raise_error }
+      end
+
+      context 'when only contains unsupported operations' do
+        let(:only) { [:operation2, :operation3, :invalid] }
+
+        it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, 'only option contains unsupported operations: "invalid". Check for typos.') }
+      end
+
+      context 'when provided only value is not an array' do
+        let(:only) { 'Invalid value' }
+
+        it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, 'only option contains value of invalid value. Value must be Array.') }
+      end
+    end
+
+    context 'when operations option is provided' do
+      let(:provided_operations) { { operations: operations } }
+
+      context 'when all operations are supported' do
+        let(:operations) { { operation2: 'irrelevant', operation3: 'irrelevant' } }
+
+        it { is_expected.not_to raise_error }
+      end
+
+      context 'when operations contains unsupported operations' do
+        let(:operations) { { operation2: 'irrelevant', operation3: 'irrelevant', invalid: 'invalid' } }
+
+        it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, 'operations option contains unsupported operations: "invalid". Check for typos.') }
+      end
+
+      context 'when provided operations value is not a hash' do
+        let(:operations) { [:one, :two, :three] }
+
+        it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, 'operations option contains value of invalid value. Value must be Hash.') }
+      end
+    end
+  end
+end
diff --git a/spec/services/mount_method/option_validators/skip_only_validator_spec.rb b/spec/services/mount_method/option_validators/skip_only_validator_spec.rb
new file mode 100644
index 00000000..7d03f124
--- /dev/null
+++ b/spec/services/mount_method/option_validators/skip_only_validator_spec.rb
@@ -0,0 +1,31 @@
+require 'spec_helper'
+
+RSpec.describe GraphqlDevise::MountMethod::OptionValidators::SkipOnlyValidator do
+  describe '#validate!' do
+    subject { -> { described_class.new(options: options).validate! } }
+
+    context 'when only `only` key is set' do
+      let(:options) { { only: 'Irrelevant value' } }
+
+      it { is_expected.not_to raise_error }
+    end
+
+    context 'when only `skip` key is set' do
+      let(:options) { { skip: 'Irrelevant value' } }
+
+      it { is_expected.not_to raise_error }
+    end
+
+    context 'when `skip` and `only` keys are set' do
+      let(:options) { { only: 'Irrelevant value', skip: 'irrelevant for specs' } }
+
+      it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, "Can't specify both `skip` and `only` options when mounting the route.") }
+    end
+
+    context 'when neither `skip` nor `only are set`' do
+      let(:options) { { irrelevant_option: 'Irrelevant value', another_option: 'irrelevant for specs' } }
+
+      it { is_expected.not_to raise_error }
+    end
+  end
+end
diff --git a/spec/services/mount_method/option_validators/supported_operations_validator_spec.rb b/spec/services/mount_method/option_validators/supported_operations_validator_spec.rb
new file mode 100644
index 00000000..a100af40
--- /dev/null
+++ b/spec/services/mount_method/option_validators/supported_operations_validator_spec.rb
@@ -0,0 +1,35 @@
+require 'spec_helper'
+
+RSpec.describe GraphqlDevise::MountMethod::OptionValidators::SupportedOperationsValidator do
+  describe '#validate!' do
+    subject { -> { described_class.new(provided_operations: provided_operations, supported_operations: supported_operations, key: key).validate! } }
+
+    let(:supported_operations) { [:operation1, :operation2, :operation3] }
+    let(:key)                  { :only }
+
+    context 'when custom operations are all supported' do
+      let(:provided_operations) { [:operation2, :operation3] }
+
+      it { is_expected.not_to raise_error }
+    end
+
+    context 'when no operations are provided' do
+      let(:provided_operations) { [] }
+
+      it { is_expected.not_to raise_error }
+    end
+
+    context 'when default_operations are empty' do
+      let(:supported_operations) { [] }
+      let(:provided_operations) { [:invalid] }
+
+      it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, 'only option contains unsupported operations: "invalid". Check for typos.') }
+    end
+
+    context 'when not all custom operations are supported' do
+      let(:provided_operations) { [:operation2, :operation3, :unsupported] }
+
+      it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, 'only option contains unsupported operations: "unsupported". Check for typos.') }
+    end
+  end
+end
diff --git a/spec/services/mount_method/options_validator_spec.rb b/spec/services/mount_method/options_validator_spec.rb
new file mode 100644
index 00000000..82dc3b4e
--- /dev/null
+++ b/spec/services/mount_method/options_validator_spec.rb
@@ -0,0 +1,36 @@
+require 'spec_helper'
+
+RSpec.describe GraphqlDevise::MountMethod::OptionsValidator do
+  describe '#validate!' do
+    subject { -> { described_class.new([validator1, validator2]).validate! } }
+
+    let(:validator1) { double(:validator1, 'validate!': nil) }
+    let(:validator2) { double(:validator2, 'validate!': nil) }
+
+    context 'when first validator fails' do
+      before { allow(validator1).to receive(:validate!).and_raise(GraphqlDevise::InvalidMountOptionsError, 'validator1 error') }
+
+      context 'when second validator fails' do
+        before { allow(validator2).to receive(:validate!).and_raise(GraphqlDevise::InvalidMountOptionsError, 'validator2 error') }
+
+        it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, 'validator1 error') }
+      end
+
+      context 'when second validator does not fail' do
+        it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, 'validator1 error') }
+      end
+    end
+
+    context 'when first validator does not fail' do
+      context 'when second validator fails' do
+        before { allow(validator2).to receive(:validate!).and_raise(GraphqlDevise::InvalidMountOptionsError, 'validator2 error') }
+
+        it { is_expected.to raise_error(GraphqlDevise::InvalidMountOptionsError, 'validator2 error') }
+      end
+
+      context 'when second validator does not fail' do
+        it { is_expected.not_to raise_error }
+      end
+    end
+  end
+end
diff --git a/spec/queries_preparer_spec.rb b/spec/services/mount_method/queries_preparer_spec.rb
similarity index 94%
rename from spec/queries_preparer_spec.rb
rename to spec/services/mount_method/queries_preparer_spec.rb
index 740032f1..b89e2030 100644
--- a/spec/queries_preparer_spec.rb
+++ b/spec/services/mount_method/queries_preparer_spec.rb
@@ -1,6 +1,6 @@
 require 'rails_helper'
 
-RSpec.describe GraphqlDevise::QueriesPreparer do
+RSpec.describe GraphqlDevise::MountMethod::QueriesPreparer do
   describe '.call' do
     subject do
       described_class.call(