diff --git a/app/services/flags/create_flag.rb b/app/services/flags/create_flag.rb
index 09addd884ec..d0089b02469 100644
--- a/app/services/flags/create_flag.rb
+++ b/app/services/flags/create_flag.rb
@@ -3,28 +3,26 @@
 class Flags::CreateFlag
   include Service::Base
 
-  contract
-  policy :invalid_access
-  policy :unique_name
-  model :flag, :instantiate_flag
-
-  transaction do
-    step :create
-    step :log
-  end
-
-  class Contract
+  contract do
     attribute :name, :string
     attribute :description, :string
     attribute :require_message, :boolean
     attribute :enabled, :boolean
     attribute :applies_to
+
     validates :name, presence: true
     validates :description, presence: true
     validates :name, length: { maximum: Flag::MAX_NAME_LENGTH }
     validates :description, length: { maximum: Flag::MAX_DESCRIPTION_LENGTH }
     validates :applies_to, inclusion: { in: -> { Flag.valid_applies_to_types } }, allow_nil: false
   end
+  policy :invalid_access
+  policy :unique_name
+  model :flag, :instantiate_flag
+  transaction do
+    step :create
+    step :log
+  end
 
   private
 
diff --git a/app/services/flags/reorder_flag.rb b/app/services/flags/reorder_flag.rb
index a306a7cd32f..bd3ae1125e4 100644
--- a/app/services/flags/reorder_flag.rb
+++ b/app/services/flags/reorder_flag.rb
@@ -5,23 +5,21 @@ VALID_DIRECTIONS = %w[up down]
 class Flags::ReorderFlag
   include Service::Base
 
-  contract
+  contract do
+    attribute :flag_id, :integer
+    attribute :direction, :string
+
+    validates :flag_id, presence: true
+    validates :direction, inclusion: { in: VALID_DIRECTIONS }
+  end
   model :flag
   policy :invalid_access
   policy :invalid_move
-
   transaction do
     step :move
     step :log
   end
 
-  class Contract
-    attribute :flag_id, :integer
-    attribute :direction, :string
-    validates :flag_id, presence: true
-    validates :direction, inclusion: { in: VALID_DIRECTIONS }
-  end
-
   private
 
   def fetch_flag(flag_id:)
diff --git a/app/services/flags/toggle_flag.rb b/app/services/flags/toggle_flag.rb
index d7c65258fd7..06afe4f4424 100644
--- a/app/services/flags/toggle_flag.rb
+++ b/app/services/flags/toggle_flag.rb
@@ -3,20 +3,18 @@
 class Flags::ToggleFlag
   include Service::Base
 
-  contract
+  contract do
+    attribute :flag_id, :integer
+
+    validates :flag_id, presence: true
+  end
   model :flag
   policy :invalid_access
-
   transaction do
     step :toggle
     step :log
   end
 
-  class Contract
-    attribute :flag_id, :integer
-    validates :flag_id, presence: true
-  end
-
   private
 
   def fetch_flag(flag_id:)
diff --git a/app/services/flags/update_flag.rb b/app/services/flags/update_flag.rb
index eaaee969d15..766d2bb701c 100644
--- a/app/services/flags/update_flag.rb
+++ b/app/services/flags/update_flag.rb
@@ -3,30 +3,28 @@
 class Flags::UpdateFlag
   include Service::Base
 
-  contract
-  model :flag
-  policy :not_system
-  policy :not_used
-  policy :invalid_access
-  policy :unique_name
-
-  transaction do
-    step :update
-    step :log
-  end
-
-  class Contract
+  contract do
     attribute :name, :string
     attribute :description, :string
     attribute :require_message, :boolean
     attribute :enabled, :boolean
     attribute :applies_to
+
     validates :name, presence: true
     validates :description, presence: true
     validates :name, length: { maximum: Flag::MAX_NAME_LENGTH }
     validates :description, length: { maximum: Flag::MAX_DESCRIPTION_LENGTH }
     validates :applies_to, inclusion: { in: -> { Flag.valid_applies_to_types } }, allow_nil: false
   end
+  model :flag
+  policy :not_system
+  policy :not_used
+  policy :invalid_access
+  policy :unique_name
+  transaction do
+    step :update
+    step :log
+  end
 
   private
 
diff --git a/app/services/update_site_setting.rb b/app/services/update_site_setting.rb
index 0b4f28ff1f3..70f2d1d6325 100644
--- a/app/services/update_site_setting.rb
+++ b/app/services/update_site_setting.rb
@@ -4,20 +4,18 @@ class UpdateSiteSetting
   include Service::Base
 
   policy :current_user_is_admin
-  contract
-  step :convert_name_to_sym
-  policy :setting_is_visible
-  policy :setting_is_configurable
-  step :cleanup_value
-  step :save
-
-  class Contract
+  contract do
     attribute :setting_name
     attribute :new_value
     attribute :allow_changing_hidden, :boolean, default: false
 
     validates :setting_name, presence: true
   end
+  step :convert_name_to_sym
+  policy :setting_is_visible
+  policy :setting_is_configurable
+  step :cleanup_value
+  step :save
 
   private
 
diff --git a/app/services/user/silence.rb b/app/services/user/silence.rb
index 778afd4cceb..afc87131942 100644
--- a/app/services/user/silence.rb
+++ b/app/services/user/silence.rb
@@ -3,16 +3,7 @@
 class User::Silence
   include Service::Base
 
-  contract
-  model :user
-  policy :not_silenced_already, class_name: User::Policy::NotAlreadySilenced
-  model :users
-  policy :can_silence_all_users
-  step :silence
-  model :post, optional: true
-  step :perform_post_action
-
-  class Contract
+  contract do
     attribute :user_id, :integer
     attribute :reason, :string
     attribute :message, :string
@@ -28,6 +19,13 @@ class User::Silence
     validates :other_user_ids, length: { maximum: User::MAX_SIMILAR_USERS }
     validates :post_action, inclusion: { in: %w[delete delete_replies edit] }, allow_blank: true
   end
+  model :user
+  policy :not_silenced_already, class_name: User::Policy::NotAlreadySilenced
+  model :users
+  policy :can_silence_all_users
+  step :silence
+  model :post, optional: true
+  step :perform_post_action
 
   private
 
diff --git a/app/services/user/suspend.rb b/app/services/user/suspend.rb
index 806f730db7b..bd08a6dc2e9 100644
--- a/app/services/user/suspend.rb
+++ b/app/services/user/suspend.rb
@@ -3,16 +3,7 @@
 class User::Suspend
   include Service::Base
 
-  contract
-  model :user
-  policy :not_suspended_already, class_name: User::Policy::NotAlreadySuspended
-  model :users
-  policy :can_suspend_all_users
-  step :suspend
-  model :post, optional: true
-  step :perform_post_action
-
-  class Contract
+  contract do
     attribute :user_id, :integer
     attribute :reason, :string
     attribute :message, :string
@@ -28,6 +19,13 @@ class User::Suspend
     validates :other_user_ids, length: { maximum: User::MAX_SIMILAR_USERS }
     validates :post_action, inclusion: { in: %w[delete delete_replies edit] }, allow_blank: true
   end
+  model :user
+  policy :not_suspended_already, class_name: User::Policy::NotAlreadySuspended
+  model :users
+  policy :can_suspend_all_users
+  step :suspend
+  model :post, optional: true
+  step :perform_post_action
 
   private
 
diff --git a/lib/service.rb b/lib/service.rb
index 8f1ef6c6973..07d39252657 100644
--- a/lib/service.rb
+++ b/lib/service.rb
@@ -11,12 +11,12 @@ module Service
   # Currently, there are 5 types of steps:
   #
   # * +contract(name = :default)+: used to validate the input parameters,
-  #   typically provided by a user calling an endpoint. A special embedded
-  #   +Contract+ class has to be defined to holds the validations. If the
-  #   validations fail, the step will fail. Otherwise, the resulting contract
-  #   will be available in +context[:contract]+. When calling +step(name)+ or
-  #   +model(name = :model)+ methods after validating a contract, the contract
-  #   should be used as an argument instead of context attributes.
+  #   typically provided by a user calling an endpoint. A block has to be
+  #   defined to hold the validations. If the validations fail, the step will
+  #   fail. Otherwise, the resulting contract will be available in
+  #   +context[:contract]+. When calling +step(name)+ or +model(name = :model)+
+  #   methods after validating a contract, the contract should be used as an
+  #   argument instead of context attributes.
   # * +model(name = :model)+: used to instantiate a model (either by building
   #   it or fetching it from the DB). If a falsy value is returned, then the
   #   step will fail. Otherwise the resulting object will be assigned in
diff --git a/lib/service/base.rb b/lib/service/base.rb
index cb7f38d5498..46559ddb858 100644
--- a/lib/service/base.rb
+++ b/lib/service/base.rb
@@ -78,10 +78,12 @@ module Service
         steps << ModelStep.new(name, step_name, optional: optional)
       end
 
-      def contract(name = :default, class_name: self::Contract, default_values_from: nil)
+      def contract(name = :default, default_values_from: nil, &block)
+        contract_class = Class.new(Service::ContractBase).tap { _1.class_eval(&block) }
+        const_set("#{name.to_s.classify.sub("Default", "")}Contract", contract_class)
         steps << ContractStep.new(
           name,
-          class_name: class_name,
+          class_name: contract_class,
           default_values_from: default_values_from,
         )
       end
@@ -214,20 +216,6 @@ module Service
     included do
       # The global context which is available from any step.
       attr_reader :context
-
-      # @!visibility private
-      # Internal class used to setup the base contract of the service.
-      self::Contract =
-        Class.new do
-          include ActiveModel::API
-          include ActiveModel::Attributes
-          include ActiveModel::AttributeMethods
-          include ActiveModel::Validations::Callbacks
-
-          def raw_attributes
-            @attributes.values_before_type_cast
-          end
-        end
     end
 
     class_methods do
@@ -306,10 +294,10 @@ module Service
     #   end
 
     # @!scope class
-    # @!method contract(name = :default, class_name: self::Contract, default_values_from: nil)
+    # @!method contract(name = :default, default_values_from: nil, &block)
     # @param name [Symbol] name for this contract
-    # @param class_name [Class] a class defining the contract
     # @param default_values_from [Symbol] name of the model to get default values from
+    # @param block [Proc] a block containing validations
     # Checks the validity of the input parameters.
     # Implements ActiveModel::Validations and ActiveModel::Attributes.
     #
@@ -317,9 +305,7 @@ module Service
     # (can be customized by providing the +name+ argument).
     #
     # @example
-    #   contract
-    #
-    #   class Contract
+    #   contract do
     #     attribute :name
     #     validates :name, presence: true
     #   end
diff --git a/lib/service/contract_base.rb b/lib/service/contract_base.rb
new file mode 100644
index 00000000000..79a0413df2b
--- /dev/null
+++ b/lib/service/contract_base.rb
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class Service::ContractBase
+  include ActiveModel::API
+  include ActiveModel::Attributes
+  include ActiveModel::AttributeMethods
+  include ActiveModel::Validations::Callbacks
+
+  def raw_attributes
+    @attributes.values_before_type_cast
+  end
+end
diff --git a/plugins/chat/app/services/chat/add_users_to_channel.rb b/plugins/chat/app/services/chat/add_users_to_channel.rb
index 318459615fe..291c0d761e6 100644
--- a/plugins/chat/app/services/chat/add_users_to_channel.rb
+++ b/plugins/chat/app/services/chat/add_users_to_channel.rb
@@ -22,33 +22,28 @@ module Chat
     #   @option params_to_create [Array<String>] usernames
     #   @option params_to_create [Array<String>] groups
     #   @return [Service::Base::Context]
-    contract
-    model :channel
-    policy :can_add_users_to_channel
-    model :target_users, optional: true
-    policy :satisfies_dms_max_users_limit,
-           class_name: Chat::DirectMessageChannel::Policy::MaxUsersExcess
-
-    transaction do
-      step :upsert_memberships
-      step :recompute_users_count
-      step :notice_channel
-    end
-
-    # @!visibility private
-    class Contract
+    contract do
       attribute :usernames, :array
       attribute :groups, :array
-
       attribute :channel_id, :integer
-      validates :channel_id, presence: true
 
+      validates :channel_id, presence: true
       validate :target_presence
 
       def target_presence
         usernames.present? || groups.present?
       end
     end
+    model :channel
+    policy :can_add_users_to_channel
+    model :target_users, optional: true
+    policy :satisfies_dms_max_users_limit,
+           class_name: Chat::DirectMessageChannel::Policy::MaxUsersExcess
+    transaction do
+      step :upsert_memberships
+      step :recompute_users_count
+      step :notice_channel
+    end
 
     private
 
@@ -128,20 +123,17 @@ module Chat
 
       return if added_users.blank?
 
-      result =
-        ::Chat::CreateMessage.call(
-          guardian: Discourse.system_user.guardian,
-          chat_channel_id: channel.id,
-          message:
-            I18n.t(
-              "chat.channel.users_invited_to_channel",
-              invited_users: added_users.map { |u| "@#{u.username}" }.join(", "),
-              inviting_user: "@#{guardian.user.username}",
-              count: added_users.count,
-            ),
-        )
-
-      fail!(failure: "Failed to notice the channel") if result.failure?
+      ::Chat::CreateMessage.call(
+        guardian: Discourse.system_user.guardian,
+        chat_channel_id: channel.id,
+        message:
+          I18n.t(
+            "chat.channel.users_invited_to_channel",
+            invited_users: added_users.map { |u| "@#{u.username}" }.join(", "),
+            inviting_user: "@#{guardian.user.username}",
+            count: added_users.count,
+          ),
+      ) { on_failure { fail!(failure: "Failed to notice the channel") } }
     end
   end
 end
diff --git a/plugins/chat/app/services/chat/auto_join_channel_batch.rb b/plugins/chat/app/services/chat/auto_join_channel_batch.rb
index 6a95cc4d314..6518e6f2e53 100644
--- a/plugins/chat/app/services/chat/auto_join_channel_batch.rb
+++ b/plugins/chat/app/services/chat/auto_join_channel_batch.rb
@@ -14,13 +14,7 @@ module Chat
   class AutoJoinChannelBatch
     include Service::Base
 
-    contract
-    model :channel
-    step :create_memberships
-    step :recalculate_user_count
-    step :publish_new_channel
-
-    class Contract
+    contract do
       # Backward-compatible attributes
       attribute :chat_channel_id, :integer
       attribute :starts_at, :integer
@@ -41,6 +35,10 @@ module Chat
         self.end_user_id ||= ends_at
       end
     end
+    model :channel
+    step :create_memberships
+    step :recalculate_user_count
+    step :publish_new_channel
 
     private
 
diff --git a/plugins/chat/app/services/chat/auto_remove/handle_category_updated.rb b/plugins/chat/app/services/chat/auto_remove/handle_category_updated.rb
index fff835bc986..6da61967c1d 100644
--- a/plugins/chat/app/services/chat/auto_remove/handle_category_updated.rb
+++ b/plugins/chat/app/services/chat/auto_remove/handle_category_updated.rb
@@ -14,7 +14,11 @@ module Chat
     class HandleCategoryUpdated
       include Service::Base
 
-      contract
+      contract do
+        attribute :category_id, :integer
+
+        validates :category_id, presence: true
+      end
       step :assign_defaults
       policy :chat_enabled
       model :category
@@ -23,12 +27,6 @@ module Chat
       step :remove_users_without_channel_permission
       step :publish
 
-      class Contract
-        attribute :category_id, :integer
-
-        validates :category_id, presence: true
-      end
-
       private
 
       def assign_defaults
diff --git a/plugins/chat/app/services/chat/auto_remove/handle_destroyed_group.rb b/plugins/chat/app/services/chat/auto_remove/handle_destroyed_group.rb
index 9d8e42b6c33..fc29b1152d0 100644
--- a/plugins/chat/app/services/chat/auto_remove/handle_destroyed_group.rb
+++ b/plugins/chat/app/services/chat/auto_remove/handle_destroyed_group.rb
@@ -21,7 +21,11 @@ module Chat
     class HandleDestroyedGroup
       include Service::Base
 
-      contract
+      contract do
+        attribute :destroyed_group_user_ids
+
+        validates :destroyed_group_user_ids, presence: true
+      end
       step :assign_defaults
       policy :chat_enabled
       policy :not_everyone_allowed
@@ -30,12 +34,6 @@ module Chat
       step :remove_users_without_channel_permission
       step :publish
 
-      class Contract
-        attribute :destroyed_group_user_ids
-
-        validates :destroyed_group_user_ids, presence: true
-      end
-
       private
 
       def assign_defaults
diff --git a/plugins/chat/app/services/chat/auto_remove/handle_user_removed_from_group.rb b/plugins/chat/app/services/chat/auto_remove/handle_user_removed_from_group.rb
index c6bdec7171e..5862ba696f8 100644
--- a/plugins/chat/app/services/chat/auto_remove/handle_user_removed_from_group.rb
+++ b/plugins/chat/app/services/chat/auto_remove/handle_user_removed_from_group.rb
@@ -20,7 +20,11 @@ module Chat
     class HandleUserRemovedFromGroup
       include Service::Base
 
-      contract
+      contract do
+        attribute :user_id, :integer
+
+        validates :user_id, presence: true
+      end
       step :assign_defaults
       policy :chat_enabled
       policy :not_everyone_allowed
@@ -30,12 +34,6 @@ module Chat
       step :remove_from_private_channels
       step :publish
 
-      class Contract
-        attribute :user_id, :integer
-
-        validates :user_id, presence: true
-      end
-
       private
 
       def assign_defaults
diff --git a/plugins/chat/app/services/chat/create_category_channel.rb b/plugins/chat/app/services/chat/create_category_channel.rb
index 5f98b74ac9f..179bcf7947b 100644
--- a/plugins/chat/app/services/chat/create_category_channel.rb
+++ b/plugins/chat/app/services/chat/create_category_channel.rb
@@ -29,17 +29,7 @@ module Chat
 
     policy :public_channels_enabled
     policy :can_create_channel
-    contract
-    model :category, :fetch_category
-    policy :category_channel_does_not_exist
-    transaction do
-      model :channel, :create_channel
-      model :membership, :create_membership
-    end
-    step :enforce_automatic_channel_memberships
-
-    # @!visibility private
-    class Contract
+    contract do
       attribute :name, :string
       attribute :description, :string
       attribute :slug, :string
@@ -55,6 +45,13 @@ module Chat
       validates :category_id, presence: true
       validates :name, length: { maximum: SiteSetting.max_topic_title_length }
     end
+    model :category
+    policy :category_channel_does_not_exist
+    transaction do
+      model :channel, :create_channel
+      model :membership, :create_membership
+    end
+    step :enforce_automatic_channel_memberships
 
     private
 
diff --git a/plugins/chat/app/services/chat/create_direct_message_channel.rb b/plugins/chat/app/services/chat/create_direct_message_channel.rb
index fd19a811a49..3af0d6df2c5 100644
--- a/plugins/chat/app/services/chat/create_direct_message_channel.rb
+++ b/plugins/chat/app/services/chat/create_direct_message_channel.rb
@@ -23,7 +23,18 @@ module Chat
     #   @option params_to_create [Boolean] upsert
     #   @return [Service::Base::Context]
 
-    contract
+    contract do
+      attribute :name, :string
+      attribute :target_usernames, :array
+      attribute :target_groups, :array
+      attribute :upsert, :boolean, default: false
+
+      validate :target_presence
+
+      def target_presence
+        target_usernames.present? || target_groups.present?
+      end
+    end
     model :target_users
     policy :can_create_direct_message
     policy :satisfies_dms_max_users_limit,
@@ -38,20 +49,6 @@ module Chat
     step :update_memberships
     step :recompute_users_count
 
-    # @!visibility private
-    class Contract
-      attribute :name, :string
-      attribute :target_usernames, :array
-      attribute :target_groups, :array
-      attribute :upsert, :boolean, default: false
-
-      validate :target_presence
-
-      def target_presence
-        target_usernames.present? || target_groups.present?
-      end
-    end
-
     private
 
     def can_create_direct_message(guardian:, target_users:)
diff --git a/plugins/chat/app/services/chat/create_message.rb b/plugins/chat/app/services/chat/create_message.rb
index 4b6170eb195..4aebe1471ed 100644
--- a/plugins/chat/app/services/chat/create_message.rb
+++ b/plugins/chat/app/services/chat/create_message.rb
@@ -22,36 +22,7 @@ module Chat
     #   @param incoming_chat_webhook [Chat::IncomingWebhook]
 
     policy :no_silenced_user
-    contract
-    model :channel
-    step :enforce_membership
-    model :membership
-    policy :allowed_to_create_message_in_channel, class_name: Chat::Channel::Policy::MessageCreation
-    model :reply, optional: true
-    policy :ensure_reply_consistency
-    model :thread, optional: true
-    policy :ensure_valid_thread_for_channel
-    policy :ensure_thread_matches_parent
-    model :uploads, optional: true
-    step :clean_message
-    model :message_instance, :instantiate_message
-
-    transaction do
-      step :create_excerpt
-      step :update_created_by_sdk
-      step :save_message
-      step :delete_drafts
-      step :post_process_thread
-      step :create_webhook_event
-      step :update_channel_last_message
-      step :update_membership_last_read
-      step :process_direct_message_channel
-    end
-    step :publish_new_thread
-    step :process
-    step :publish_user_tracking_state
-
-    class Contract
+    contract do
       attribute :chat_channel_id, :string
       attribute :in_reply_to_id, :string
       attribute :context_topic_id, :integer
@@ -71,6 +42,32 @@ module Chat
       validates :chat_channel_id, presence: true
       validates :message, presence: true, if: -> { upload_ids.blank? }
     end
+    model :channel
+    step :enforce_membership
+    model :membership
+    policy :allowed_to_create_message_in_channel, class_name: Chat::Channel::Policy::MessageCreation
+    model :reply, optional: true
+    policy :ensure_reply_consistency
+    model :thread, optional: true
+    policy :ensure_valid_thread_for_channel
+    policy :ensure_thread_matches_parent
+    model :uploads, optional: true
+    step :clean_message
+    model :message_instance, :instantiate_message
+    transaction do
+      step :create_excerpt
+      step :update_created_by_sdk
+      step :save_message
+      step :delete_drafts
+      step :post_process_thread
+      step :create_webhook_event
+      step :update_channel_last_message
+      step :update_membership_last_read
+      step :process_direct_message_channel
+    end
+    step :publish_new_thread
+    step :process
+    step :publish_user_tracking_state
 
     private
 
diff --git a/plugins/chat/app/services/chat/create_thread.rb b/plugins/chat/app/services/chat/create_thread.rb
index 0e1316de21e..e7b6f042b60 100644
--- a/plugins/chat/app/services/chat/create_thread.rb
+++ b/plugins/chat/app/services/chat/create_thread.rb
@@ -16,7 +16,14 @@ module Chat
     #   @option params_to_create [String,nil] title
     #   @return [Service::Base::Context]
 
-    contract
+    contract do
+      attribute :original_message_id, :integer
+      attribute :channel_id, :integer
+      attribute :title, :string
+
+      validates :original_message_id, :channel_id, presence: true
+      validates :title, length: { maximum: Chat::Thread::MAX_TITLE_LENGTH }
+    end
     model :channel
     policy :can_view_channel
     policy :threading_enabled_for_channel
@@ -29,16 +36,6 @@ module Chat
       step :trigger_chat_thread_created_event
     end
 
-    # @!visibility private
-    class Contract
-      attribute :original_message_id, :integer
-      attribute :channel_id, :integer
-      attribute :title, :string
-
-      validates :original_message_id, :channel_id, presence: true
-      validates :title, length: { maximum: Chat::Thread::MAX_TITLE_LENGTH }
-    end
-
     private
 
     def fetch_channel(contract:)
diff --git a/plugins/chat/app/services/chat/flag_message.rb b/plugins/chat/app/services/chat/flag_message.rb
index 0bdea682e13..ad610dddebe 100644
--- a/plugins/chat/app/services/chat/flag_message.rb
+++ b/plugins/chat/app/services/chat/flag_message.rb
@@ -26,27 +26,22 @@ module Chat
     #     the force_review option.
 
     #   @return [Service::Base::Context]
-    contract
-    model :message
-    policy :can_flag_message_in_channel
-    step :flag_message
-
-    # @!visibility private
-    class Contract
+    contract do
       attribute :message_id, :integer
-      validates :message_id, presence: true
-
       attribute :channel_id, :integer
-      validates :channel_id, presence: true
-
       attribute :flag_type_id, :integer
-      validates :flag_type_id, inclusion: { in: ->(_flag_type) { ::ReviewableScore.types.values } }
-
       attribute :message, :string
       attribute :is_warning, :boolean
       attribute :take_action, :boolean
       attribute :queue_for_review, :boolean
+
+      validates :message_id, presence: true
+      validates :channel_id, presence: true
+      validates :flag_type_id, inclusion: { in: ->(_flag_type) { ::ReviewableScore.types.values } }
     end
+    model :message
+    policy :can_flag_message_in_channel
+    step :flag_message
 
     private
 
diff --git a/plugins/chat/app/services/chat/invite_users_to_channel.rb b/plugins/chat/app/services/chat/invite_users_to_channel.rb
index e2346f42f7a..1a492af4584 100644
--- a/plugins/chat/app/services/chat/invite_users_to_channel.rb
+++ b/plugins/chat/app/services/chat/invite_users_to_channel.rb
@@ -16,23 +16,19 @@ module Chat
     #   @option optional_params [Integer, nil] message_id
     #   @return [Service::Base::Context]
 
-    contract
+    contract do
+      attribute :user_ids, :array
+      attribute :channel_id, :integer
+      attribute :message_id, :integer
+
+      validates :user_ids, presence: true
+      validates :channel_id, presence: true
+    end
     model :channel
     policy :can_view_channel
     model :users, optional: true
     step :send_invite_notifications
 
-    # @!visibility private
-    class Contract
-      attribute :user_ids, :array
-      validates :user_ids, presence: true
-
-      attribute :channel_id, :integer
-      validates :channel_id, presence: true
-
-      attribute :message_id, :integer
-    end
-
     private
 
     def fetch_channel(contract:)
diff --git a/plugins/chat/app/services/chat/leave_channel.rb b/plugins/chat/app/services/chat/leave_channel.rb
index f905eb04ff6..63afd9ab3df 100644
--- a/plugins/chat/app/services/chat/leave_channel.rb
+++ b/plugins/chat/app/services/chat/leave_channel.rb
@@ -17,17 +17,15 @@ module Chat
     #   @param [Integer] channel_id of the channel
 
     #   @return [Service::Base::Context]
-    contract
+    contract do
+      attribute :channel_id, :integer
+
+      validates :channel_id, presence: true
+    end
     model :channel
     step :leave
     step :recompute_users_count
 
-    # @!visibility private
-    class Contract
-      attribute :channel_id, :integer
-      validates :channel_id, presence: true
-    end
-
     private
 
     def fetch_channel(contract:)
diff --git a/plugins/chat/app/services/chat/list_channel_messages.rb b/plugins/chat/app/services/chat/list_channel_messages.rb
index 62b3770ccad..1ec134f8e98 100644
--- a/plugins/chat/app/services/chat/list_channel_messages.rb
+++ b/plugins/chat/app/services/chat/list_channel_messages.rb
@@ -15,11 +15,34 @@ module Chat
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
 
-    contract
+    contract do
+      attribute :channel_id, :integer
+      attribute :page_size, :integer
+
+      # If this is not present, then we just fetch messages with page_size
+      # and direction.
+      attribute :target_message_id, :integer # (optional)
+      attribute :direction, :string # (optional)
+      attribute :fetch_from_last_read, :boolean # (optional)
+      attribute :target_date, :string # (optional)
+
+      validates :channel_id, presence: true
+      validates :page_size,
+                numericality: {
+                  less_than_or_equal_to: ::Chat::MessagesQuery::MAX_PAGE_SIZE,
+                  only_integer: true,
+                },
+                allow_nil: true
+      validates :direction,
+                inclusion: {
+                  in: Chat::MessagesQuery::VALID_DIRECTIONS,
+                },
+                allow_nil: true
+    end
 
     model :channel
     policy :can_view_channel
-    step :fetch_optional_membership
+    model :membership, optional: true
     step :enabled_threads?
     step :determine_target_message_id
     policy :target_message_exists
@@ -31,40 +54,14 @@ module Chat
     step :update_membership_last_viewed_at
     step :update_user_last_channel
 
-    class Contract
-      attribute :channel_id, :integer
-      validates :channel_id, presence: true
-
-      attribute :page_size, :integer
-      validates :page_size,
-                numericality: {
-                  less_than_or_equal_to: ::Chat::MessagesQuery::MAX_PAGE_SIZE,
-                  only_integer: true,
-                },
-                allow_nil: true
-
-      # If this is not present, then we just fetch messages with page_size
-      # and direction.
-      attribute :target_message_id, :integer # (optional)
-      attribute :direction, :string # (optional)
-      attribute :fetch_from_last_read, :boolean # (optional)
-      attribute :target_date, :string # (optional)
-
-      validates :direction,
-                inclusion: {
-                  in: Chat::MessagesQuery::VALID_DIRECTIONS,
-                },
-                allow_nil: true
-    end
-
     private
 
     def fetch_channel(contract:)
       ::Chat::Channel.includes(:chatable).find_by(id: contract.channel_id)
     end
 
-    def fetch_optional_membership(channel:, guardian:)
-      context.membership = channel.membership_for(guardian.user)
+    def fetch_membership(channel:, guardian:)
+      channel.membership_for(guardian.user)
     end
 
     def enabled_threads?(channel:)
diff --git a/plugins/chat/app/services/chat/list_channel_thread_messages.rb b/plugins/chat/app/services/chat/list_channel_thread_messages.rb
index 152e4268678..63fc584ff57 100644
--- a/plugins/chat/app/services/chat/list_channel_thread_messages.rb
+++ b/plugins/chat/app/services/chat/list_channel_thread_messages.rb
@@ -15,19 +15,8 @@ module Chat
     #   @option optional_params [Integer] thread_id
     #   @return [Service::Base::Context]
 
-    contract
-
-    model :thread
-    policy :can_view_thread
-    step :fetch_optional_membership
-    step :determine_target_message_id
-    policy :target_message_exists
-    step :fetch_messages
-
-    class Contract
+    contract do
       attribute :thread_id, :integer
-      validates :thread_id, presence: true
-
       # If this is not present, then we just fetch messages with page_size
       # and direction.
       attribute :target_message_id, :integer # (optional)
@@ -38,6 +27,7 @@ module Chat
       attribute :fetch_from_first_message, :boolean # (optional)
       attribute :target_date, :string # (optional)
 
+      validates :thread_id, presence: true
       validates :direction,
                 inclusion: {
                   in: Chat::MessagesQuery::VALID_DIRECTIONS,
@@ -50,13 +40,15 @@ module Chat
                 },
                 allow_nil: true
     end
+    model :thread
+    policy :can_view_thread
+    model :membership, optional: true
+    step :determine_target_message_id
+    policy :target_message_exists
+    model :messages, optional: true
 
     private
 
-    def fetch_optional_membership(thread:, guardian:)
-      context.membership = thread.membership_for(guardian.user)
-    end
-
     def fetch_thread(contract:)
       ::Chat::Thread.strict_loading.includes(channel: :chatable).find_by(id: contract.thread_id)
     end
@@ -65,6 +57,10 @@ module Chat
       guardian.user == Discourse.system_user || guardian.can_preview_chat_channel?(thread.channel)
     end
 
+    def fetch_membership(thread:, guardian:)
+      thread.membership_for(guardian.user)
+    end
+
     def determine_target_message_id(contract:, membership:, guardian:, thread:)
       if contract.fetch_from_last_message
         context.target_message_id = thread.last_message_id
@@ -106,7 +102,7 @@ module Chat
       context.can_load_more_past = messages_data[:can_load_more_past]
       context.can_load_more_future = messages_data[:can_load_more_future]
 
-      context.messages = [
+      [
         messages_data[:messages],
         messages_data[:past_messages]&.reverse,
         messages_data[:target_message],
diff --git a/plugins/chat/app/services/chat/lookup_channel_threads.rb b/plugins/chat/app/services/chat/lookup_channel_threads.rb
index 261f35bb916..2c57dc76444 100644
--- a/plugins/chat/app/services/chat/lookup_channel_threads.rb
+++ b/plugins/chat/app/services/chat/lookup_channel_threads.rb
@@ -24,7 +24,19 @@ module Chat
     #   @param [Integer] offset
     #   @return [Service::Base::Context]
 
-    contract
+    contract do
+      attribute :channel_id, :integer
+      attribute :limit, :integer
+      attribute :offset, :integer
+
+      validates :channel_id, presence: true
+      validates :limit,
+                numericality: {
+                  less_than_or_equal_to: THREADS_LIMIT,
+                  only_integer: true,
+                },
+                allow_nil: true
+    end
     step :set_limit
     step :set_offset
     model :channel
@@ -36,22 +48,6 @@ module Chat
     step :fetch_participants
     step :build_load_more_url
 
-    # @!visibility private
-    class Contract
-      attribute :channel_id, :integer
-      validates :channel_id, presence: true
-
-      attribute :limit, :integer
-      validates :limit,
-                numericality: {
-                  less_than_or_equal_to: THREADS_LIMIT,
-                  only_integer: true,
-                },
-                allow_nil: true
-
-      attribute :offset, :integer
-    end
-
     private
 
     def set_limit(contract:)
diff --git a/plugins/chat/app/services/chat/lookup_thread.rb b/plugins/chat/app/services/chat/lookup_thread.rb
index 937993bfcd5..f8aa427d3b5 100644
--- a/plugins/chat/app/services/chat/lookup_thread.rb
+++ b/plugins/chat/app/services/chat/lookup_thread.rb
@@ -16,20 +16,17 @@ module Chat
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
 
-    contract
-    model :thread, :fetch_thread
-    policy :invalid_access
-    policy :threading_enabled_for_channel
-    step :fetch_membership
-    step :fetch_participants
-
-    # @!visibility private
-    class Contract
+    contract do
       attribute :thread_id, :integer
       attribute :channel_id, :integer
 
       validates :thread_id, :channel_id, presence: true
     end
+    model :thread
+    policy :invalid_access
+    policy :threading_enabled_for_channel
+    model :membership, optional: true
+    model :participants, optional: true
 
     private
 
@@ -50,11 +47,11 @@ module Chat
     end
 
     def fetch_membership(thread:, guardian:)
-      context.membership = thread.membership_for(guardian.user)
+      thread.membership_for(guardian.user)
     end
 
     def fetch_participants(thread:)
-      context.participants = ::Chat::ThreadParticipantQuery.call(thread_ids: [thread.id])[thread.id]
+      ::Chat::ThreadParticipantQuery.call(thread_ids: [thread.id])[thread.id]
     end
   end
 end
diff --git a/plugins/chat/app/services/chat/lookup_user_threads.rb b/plugins/chat/app/services/chat/lookup_user_threads.rb
index 75d311e1553..571c9f7c7d1 100644
--- a/plugins/chat/app/services/chat/lookup_user_threads.rb
+++ b/plugins/chat/app/services/chat/lookup_user_threads.rb
@@ -20,7 +20,10 @@ module Chat
     #   @param [Integer] offset
     #   @return [Service::Base::Context]
 
-    contract
+    contract do
+      attribute :limit, :integer
+      attribute :offset, :integer
+    end
     step :set_limit
     step :set_offset
     model :threads
@@ -29,12 +32,6 @@ module Chat
     step :fetch_participants
     step :build_load_more_url
 
-    # @!visibility private
-    class Contract
-      attribute :limit, :integer
-      attribute :offset, :integer
-    end
-
     private
 
     def set_limit(contract:)
diff --git a/plugins/chat/app/services/chat/mark_thread_title_prompt_seen.rb b/plugins/chat/app/services/chat/mark_thread_title_prompt_seen.rb
index bd102747818..4a03d07febf 100644
--- a/plugins/chat/app/services/chat/mark_thread_title_prompt_seen.rb
+++ b/plugins/chat/app/services/chat/mark_thread_title_prompt_seen.rb
@@ -21,19 +21,16 @@ module Chat
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
 
-    contract
-    model :thread
-    policy :threading_enabled_for_channel
-    policy :can_view_channel
-    transaction { step :create_or_update_membership }
-
-    # @!visibility private
-    class Contract
+    contract do
       attribute :thread_id, :integer
       attribute :channel_id, :integer
 
       validates :thread_id, :channel_id, presence: true
     end
+    model :thread
+    policy :threading_enabled_for_channel
+    policy :can_view_channel
+    transaction { step :create_or_update_membership }
 
     private
 
diff --git a/plugins/chat/app/services/chat/restore_message.rb b/plugins/chat/app/services/chat/restore_message.rb
index d5bf0d835fe..757d672ba4c 100644
--- a/plugins/chat/app/services/chat/restore_message.rb
+++ b/plugins/chat/app/services/chat/restore_message.rb
@@ -17,7 +17,13 @@ module Chat
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
 
-    contract
+    contract do
+      attribute :message_id, :integer
+      attribute :channel_id, :integer
+
+      validates :message_id, presence: true
+      validates :channel_id, presence: true
+    end
     model :message
     policy :invalid_access
     transaction do
@@ -27,14 +33,6 @@ module Chat
     end
     step :publish_events
 
-    # @!visibility private
-    class Contract
-      attribute :message_id, :integer
-      attribute :channel_id, :integer
-      validates :message_id, presence: true
-      validates :channel_id, presence: true
-    end
-
     private
 
     def fetch_message(contract:)
diff --git a/plugins/chat/app/services/chat/search_chatable.rb b/plugins/chat/app/services/chat/search_chatable.rb
index 37566821905..47c29aeb168 100644
--- a/plugins/chat/app/services/chat/search_chatable.rb
+++ b/plugins/chat/app/services/chat/search_chatable.rb
@@ -16,16 +16,7 @@ module Chat
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
 
-    contract
-    step :clean_term
-    model :memberships, optional: true
-    model :users, optional: true
-    model :groups, optional: true
-    model :category_channels, optional: true
-    model :direct_message_channels, optional: true
-
-    # @!visibility private
-    class Contract
+    contract do
       attribute :term, :string, default: ""
       attribute :include_users, :boolean, default: true
       attribute :include_groups, :boolean, default: true
@@ -33,6 +24,12 @@ module Chat
       attribute :include_direct_message_channels, :boolean, default: true
       attribute :excluded_memberships_channel_id, :integer
     end
+    step :clean_term
+    model :memberships, optional: true
+    model :users, optional: true
+    model :groups, optional: true
+    model :category_channels, optional: true
+    model :direct_message_channels, optional: true
 
     private
 
diff --git a/plugins/chat/app/services/chat/stop_message_streaming.rb b/plugins/chat/app/services/chat/stop_message_streaming.rb
index 730c93b749d..ce35b04b70d 100644
--- a/plugins/chat/app/services/chat/stop_message_streaming.rb
+++ b/plugins/chat/app/services/chat/stop_message_streaming.rb
@@ -13,7 +13,11 @@ module Chat
     #   @param [Integer] message_id
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
-    contract
+    contract do
+      attribute :message_id, :integer
+
+      validates :message_id, presence: true
+    end
     model :message
     step :enforce_membership
     model :membership
@@ -21,13 +25,6 @@ module Chat
     step :stop_message_streaming
     step :publish_message_streaming_state
 
-    # @!visibility private
-    class Contract
-      attribute :message_id, :integer
-
-      validates :message_id, presence: true
-    end
-
     private
 
     def fetch_message(contract:)
diff --git a/plugins/chat/app/services/chat/tracking_state.rb b/plugins/chat/app/services/chat/tracking_state.rb
index 5bfd53ffe2a..7704b29821f 100644
--- a/plugins/chat/app/services/chat/tracking_state.rb
+++ b/plugins/chat/app/services/chat/tracking_state.rb
@@ -33,26 +33,17 @@ module Chat
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
 
-    contract
-    step :cast_thread_and_channel_ids_to_integer
-    model :report
-
-    # @!visibility private
-    class Contract
-      attribute :channel_ids, default: []
-      attribute :thread_ids, default: []
+    contract do
+      attribute :channel_ids, :array, default: []
+      attribute :thread_ids, :array, default: []
       attribute :include_missing_memberships, default: false
       attribute :include_threads, default: false
       attribute :include_read, default: true
     end
+    model :report
 
     private
 
-    def cast_thread_and_channel_ids_to_integer(contract:)
-      contract.thread_ids = contract.thread_ids.map(&:to_i)
-      contract.channel_ids = contract.channel_ids.map(&:to_i)
-    end
-
     def fetch_report(contract:, guardian:)
       ::Chat::TrackingStateReportQuery.call(
         guardian: guardian,
diff --git a/plugins/chat/app/services/chat/trash_message.rb b/plugins/chat/app/services/chat/trash_message.rb
index 6bb8100bc1e..51be333c270 100644
--- a/plugins/chat/app/services/chat/trash_message.rb
+++ b/plugins/chat/app/services/chat/trash_message.rb
@@ -17,7 +17,13 @@ module Chat
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
 
-    contract
+    contract do
+      attribute :message_id, :integer
+      attribute :channel_id, :integer
+
+      validates :message_id, presence: true
+      validates :channel_id, presence: true
+    end
     model :message
     policy :invalid_access
     transaction do
@@ -29,14 +35,6 @@ module Chat
     end
     step :publish_events
 
-    # @!visibility private
-    class Contract
-      attribute :message_id, :integer
-      attribute :channel_id, :integer
-      validates :message_id, presence: true
-      validates :channel_id, presence: true
-    end
-
     private
 
     def fetch_message(contract:)
diff --git a/plugins/chat/app/services/chat/trash_messages.rb b/plugins/chat/app/services/chat/trash_messages.rb
index 1593752e793..eb278cde763 100644
--- a/plugins/chat/app/services/chat/trash_messages.rb
+++ b/plugins/chat/app/services/chat/trash_messages.rb
@@ -17,7 +17,13 @@ module Chat
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
 
-    contract
+    contract do
+      attribute :channel_id, :integer
+      attribute :message_ids, :array
+
+      validates :channel_id, presence: true
+      validates :message_ids, length: { minimum: 1, maximum: 50 }
+    end
     model :messages
     policy :can_delete_all_chat_messages
     transaction do
@@ -29,14 +35,6 @@ module Chat
     end
     step :publish_events
 
-    # @!visibility private
-    class Contract
-      attribute :channel_id, :integer
-      attribute :message_ids, :array
-      validates :channel_id, presence: true
-      validates :message_ids, length: { minimum: 1, maximum: 50 }
-    end
-
     private
 
     def fetch_messages(contract:)
diff --git a/plugins/chat/app/services/chat/unfollow_channel.rb b/plugins/chat/app/services/chat/unfollow_channel.rb
index 5f58c3ebb96..851ef0260d0 100644
--- a/plugins/chat/app/services/chat/unfollow_channel.rb
+++ b/plugins/chat/app/services/chat/unfollow_channel.rb
@@ -17,15 +17,13 @@ module Chat
     #   @param [Integer] channel_id of the channel
 
     #   @return [Service::Base::Context]
-    contract
-    model :channel
-    step :unfollow
-
-    # @!visibility private
-    class Contract
+    contract do
       attribute :channel_id, :integer
+
       validates :channel_id, presence: true
     end
+    model :channel
+    step :unfollow
 
     private
 
diff --git a/plugins/chat/app/services/chat/update_channel.rb b/plugins/chat/app/services/chat/update_channel.rb
index fbf920fbd89..38a3faad535 100644
--- a/plugins/chat/app/services/chat/update_channel.rb
+++ b/plugins/chat/app/services/chat/update_channel.rb
@@ -32,17 +32,9 @@ module Chat
     #   @option params_to_edit [Boolean] allow_channel_wide_mentions Allow the use of @here and @all in the channel.
     #   @return [Service::Base::Context]
 
-    model :channel, :fetch_channel
+    model :channel
     policy :check_channel_permission
-    contract default_values_from: :channel
-    step :update_channel
-    step :mark_all_threads_as_read_if_needed
-    step :update_site_settings_if_needed
-    step :publish_channel_update
-    step :auto_join_users_if_needed
-
-    # @!visibility private
-    class Contract
+    contract(default_values_from: :channel) do
       attribute :name, :string
       attribute :description, :string
       attribute :slug, :string
@@ -56,6 +48,11 @@ module Chat
         )
       end
     end
+    step :update_channel
+    step :mark_all_threads_as_read_if_needed
+    step :update_site_settings_if_needed
+    step :publish_channel_update
+    step :auto_join_users_if_needed
 
     private
 
diff --git a/plugins/chat/app/services/chat/update_channel_status.rb b/plugins/chat/app/services/chat/update_channel_status.rb
index 8719406d07c..1816599846c 100644
--- a/plugins/chat/app/services/chat/update_channel_status.rb
+++ b/plugins/chat/app/services/chat/update_channel_status.rb
@@ -16,15 +16,13 @@ module Chat
     #   @return [Service::Base::Context]
 
     model :channel, :fetch_channel
-    contract
-    policy :check_channel_permission
-    step :change_status
-
-    # @!visibility private
-    class Contract
+    contract do
       attribute :status
+
       validates :status, inclusion: { in: Chat::Channel.editable_statuses.keys }
     end
+    policy :check_channel_permission
+    step :change_status
 
     private
 
diff --git a/plugins/chat/app/services/chat/update_message.rb b/plugins/chat/app/services/chat/update_message.rb
index 2bf2ecbb746..8bbc5fc36b2 100644
--- a/plugins/chat/app/services/chat/update_message.rb
+++ b/plugins/chat/app/services/chat/update_message.rb
@@ -15,7 +15,17 @@ module Chat
     #   @param message [String]
     #   @param upload_ids [Array<Integer>] IDs of uploaded documents
 
-    contract
+    contract do
+      attribute :message_id, :string
+      attribute :message, :string
+      attribute :upload_ids, :array
+      attribute :streaming, :boolean, default: false
+      attribute :strip_whitespaces, :boolean, default: true
+      attribute :process_inline, :boolean, default: Rails.env.test?
+
+      validates :message_id, presence: true
+      validates :message, presence: true, if: -> { upload_ids.blank? }
+    end
     model :message
     model :uploads, optional: true
     step :enforce_membership
@@ -23,7 +33,6 @@ module Chat
     policy :can_modify_channel_message
     policy :can_modify_message
     step :clean_message
-
     transaction do
       step :modify_message
       step :update_excerpt
@@ -32,22 +41,6 @@ module Chat
       step :publish
     end
 
-    class Contract
-      attribute :message_id, :string
-      validates :message_id, presence: true
-
-      attribute :message, :string
-      validates :message, presence: true, if: -> { upload_ids.blank? }
-
-      attribute :upload_ids, :array
-
-      attribute :streaming, :boolean, default: false
-
-      attribute :strip_whitespaces, :boolean, default: true
-
-      attribute :process_inline, :boolean, default: Rails.env.test?
-    end
-
     private
 
     def enforce_membership(guardian:, message:)
diff --git a/plugins/chat/app/services/chat/update_thread.rb b/plugins/chat/app/services/chat/update_thread.rb
index dccd3160986..3d0db4a1059 100644
--- a/plugins/chat/app/services/chat/update_thread.rb
+++ b/plugins/chat/app/services/chat/update_thread.rb
@@ -19,22 +19,19 @@ module Chat
     #   @option params_to_edit [String,nil] title
     #   @return [Service::Base::Context]
 
-    contract
-    model :thread, :fetch_thread
-    policy :can_view_channel
-    policy :can_edit_thread
-    policy :threading_enabled_for_channel
-    step :update
-    step :publish_metadata
-
-    # @!visibility private
-    class Contract
+    contract do
       attribute :thread_id, :integer
       attribute :title, :string
 
       validates :thread_id, presence: true
       validates :title, length: { maximum: Chat::Thread::MAX_TITLE_LENGTH }
     end
+    model :thread
+    policy :can_view_channel
+    policy :can_edit_thread
+    policy :threading_enabled_for_channel
+    step :update
+    step :publish_metadata
 
     private
 
diff --git a/plugins/chat/app/services/chat/update_thread_notification_settings.rb b/plugins/chat/app/services/chat/update_thread_notification_settings.rb
index 6d7b1266f13..4cdeae35a68 100644
--- a/plugins/chat/app/services/chat/update_thread_notification_settings.rb
+++ b/plugins/chat/app/services/chat/update_thread_notification_settings.rb
@@ -23,25 +23,21 @@ module Chat
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
 
-    contract
-    model :thread, :fetch_thread
-    policy :can_view_channel
-    policy :threading_enabled_for_channel
-    transaction { step :create_or_update_membership }
-
-    # @!visibility private
-    class Contract
+    contract do
       attribute :thread_id, :integer
       attribute :channel_id, :integer
       attribute :notification_level, :integer
 
       validates :thread_id, :channel_id, :notification_level, presence: true
-
       validates :notification_level,
                 inclusion: {
                   in: Chat::UserChatThreadMembership.notification_levels.values,
                 }
     end
+    model :thread, :fetch_thread
+    policy :can_view_channel
+    policy :threading_enabled_for_channel
+    transaction { step :create_or_update_membership }
 
     private
 
diff --git a/plugins/chat/app/services/chat/update_user_channel_last_read.rb b/plugins/chat/app/services/chat/update_user_channel_last_read.rb
index 94600d55ab8..45629daa820 100644
--- a/plugins/chat/app/services/chat/update_user_channel_last_read.rb
+++ b/plugins/chat/app/services/chat/update_user_channel_last_read.rb
@@ -15,7 +15,12 @@ module Chat
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
 
-    contract
+    contract do
+      attribute :message_id, :integer
+      attribute :channel_id, :integer
+
+      validates :message_id, :channel_id, presence: true
+    end
     model :channel
     model :membership
     policy :invalid_access
@@ -27,14 +32,6 @@ module Chat
     end
     step :publish_new_last_read_to_clients
 
-    # @!visibility private
-    class Contract
-      attribute :message_id, :integer
-      attribute :channel_id, :integer
-
-      validates :message_id, :channel_id, presence: true
-    end
-
     private
 
     def fetch_channel(contract:)
diff --git a/plugins/chat/app/services/chat/update_user_thread_last_read.rb b/plugins/chat/app/services/chat/update_user_thread_last_read.rb
index 5004416503a..6fcb9d0e73d 100644
--- a/plugins/chat/app/services/chat/update_user_thread_last_read.rb
+++ b/plugins/chat/app/services/chat/update_user_thread_last_read.rb
@@ -17,7 +17,13 @@ module Chat
     #   @param [Guardian] guardian
     #   @return [Service::Base::Context]
 
-    contract
+    contract do
+      attribute :channel_id, :integer
+      attribute :thread_id, :integer
+      attribute :message_id, :integer
+
+      validates :thread_id, :channel_id, presence: true
+    end
     model :thread
     policy :invalid_access
     model :membership
@@ -27,15 +33,6 @@ module Chat
     step :mark_thread_read
     step :publish_new_last_read_to_clients
 
-    # @!visibility private
-    class Contract
-      attribute :channel_id, :integer
-      attribute :thread_id, :integer
-      attribute :message_id, :integer
-
-      validates :thread_id, :channel_id, presence: true
-    end
-
     private
 
     def fetch_thread(contract:)
diff --git a/plugins/chat/app/services/chat/upsert_draft.rb b/plugins/chat/app/services/chat/upsert_draft.rb
index 392ef5621b3..d6b4a5db889 100644
--- a/plugins/chat/app/services/chat/upsert_draft.rb
+++ b/plugins/chat/app/services/chat/upsert_draft.rb
@@ -20,20 +20,17 @@ module Chat
     #   @param [String] json object as string containing the data of the draft (message, uploads, replyToMsg and editing keys)
     #   @option [Integer] thread_id of the channel
     #   @return [Service::Base::Context]
-    contract
-    model :channel
-    policy :can_upsert_draft
-    step :check_thread_exists
-    step :upsert_draft
-
-    # @!visibility private
-    class Contract
+    contract do
       attribute :channel_id, :integer
       validates :channel_id, presence: true
 
       attribute :thread_id, :integer
       attribute :data, :string
     end
+    model :channel
+    policy :can_upsert_draft
+    step :check_thread_exists
+    step :upsert_draft
 
     private
 
diff --git a/spec/lib/service/runner_spec.rb b/spec/lib/service/runner_spec.rb
index 1d8cd6680bb..b9d98c66b03 100644
--- a/spec/lib/service/runner_spec.rb
+++ b/spec/lib/service/runner_spec.rb
@@ -38,18 +38,17 @@ RSpec.describe Service::Runner do
   class FailedContractService
     include Service::Base
 
-    class Contract
+    contract do
       attribute :test
+
       validates :test, presence: true
     end
-
-    contract
   end
 
   class SuccessContractService
     include Service::Base
 
-    contract
+    contract {}
   end
 
   class FailureWithModelService
diff --git a/spec/lib/steps_inspector_spec.rb b/spec/lib/steps_inspector_spec.rb
index 38227239a7d..dcc0917460b 100644
--- a/spec/lib/steps_inspector_spec.rb
+++ b/spec/lib/steps_inspector_spec.rb
@@ -6,18 +6,16 @@ RSpec.describe StepsInspector do
 
     model :model
     policy :policy
-    contract
+    contract do
+      attribute :parameter
+
+      validates :parameter, presence: true
+    end
     transaction do
       step :in_transaction_step_1
       step :in_transaction_step_2
     end
     step :final_step
-
-    class Contract
-      attribute :parameter
-
-      validates :parameter, presence: true
-    end
   end
 
   subject(:inspector) { described_class.new(result) }