Extend modules instead of inheriting classes

README.md

@@ -89,7 +89,9 @@ require "mcp"
 require "mcp/server/transports/stdio_transport"
 
 # Create a simple tool
-class ExampleTool < MCP::Tool
+module ExampleTool
+  extend MCP::Tool
+
   description "A simple example tool that echoes back its arguments"
   input_schema(
     properties: {
@@ -275,7 +277,9 @@ This gem provides a `MCP::Tool` class that can be used to create tools in two wa
 1. As a class definition:
 
 ```ruby
-class MyTool < MCP::Tool
+module MyTool
+  extend MCP::Tool
+
   description "This tool performs specific functionality..."
   input_schema(
     properties: {
@@ -338,7 +342,9 @@ The `MCP::Prompt` class provides two ways to create prompts:
 1. As a class definition with metadata:
 
 ```ruby
-class MyPrompt < MCP::Prompt
+module MyPrompt
+  extend MCP::Prompt
+
   prompt_name "my_prompt"  # Optional - defaults to underscored class name
   description "This prompt performs specific functionality..."
   arguments [

lib/mcp/prompt.rb

@@ -2,58 +2,16 @@
 # frozen_string_literal: true
 
 module MCP
-  class Prompt
-    class << self
-      NOT_SET = Object.new
-
-      attr_reader :description_value
-      attr_reader :arguments_value
-
-      def template(args, server_context:)
-        raise NotImplementedError, "Subclasses must implement template"
-      end
-
-      def to_h
-        { name: name_value, description: description_value, arguments: arguments_value.map(&:to_h) }.compact
-      end
-
-      def inherited(subclass)
-        super
-        subclass.instance_variable_set(:@name_value, nil)
-        subclass.instance_variable_set(:@description_value, nil)
-        subclass.instance_variable_set(:@arguments_value, nil)
-      end
-
-      def prompt_name(value = NOT_SET)
-        if value == NOT_SET
-          @name_value
-        else
-          @name_value = value
-        end
-      end
+  module Prompt
+    NOT_SET = Object.new
 
-      def name_value
-        @name_value || StringUtils.handle_from_class_name(name)
-      end
-
-      def description(value = NOT_SET)
-        if value == NOT_SET
-          @description_value
-        else
-          @description_value = value
-        end
-      end
-
-      def arguments(value = NOT_SET)
-        if value == NOT_SET
-          @arguments_value
-        else
-          @arguments_value = value
-        end
-      end
+    attr_reader :description_value
+    attr_reader :arguments_value
 
+    class << self
       def define(name: nil, description: nil, arguments: [], &block)
-        Class.new(self) do
+        Module.new do
+          extend Prompt
           prompt_name name
           description description
           arguments arguments
@@ -62,21 +20,64 @@ def define(name: nil, description: nil, arguments: [], &block)
           end
         end
       end
+    end
 
-      def validate_arguments!(args)
-        missing = required_args - args.keys
-        return if missing.empty?
+    def template(args, server_context:)
+      raise NotImplementedError, "Prompts must implement template"
+    end
+
+    def to_h
+      { name: name_value, description: description_value, arguments: arguments_value.map(&:to_h) }.compact
+    end
 
-        raise MCP::Server::RequestHandlerError.new(
-          "Missing required arguments: #{missing.join(", ")}", nil, error_type: :missing_required_arguments
-        )
+    def extended(mod)
+      super
+      mod.instance_variable_set(:@name_value, nil)
+      mod.instance_variable_set(:@description_value, nil)
+      mod.instance_variable_set(:@arguments_value, nil)
+    end
+
+    def prompt_name(value = NOT_SET)
+      if value == NOT_SET
+        @name_value
+      else
+        @name_value = value
       end
+    end
+
+    def name_value
+      @name_value || StringUtils.handle_from_class_name(name)
+    end
 
-      private
+    def description(value = NOT_SET)
+      if value == NOT_SET
+        @description_value
+      else
+        @description_value = value
+      end
+    end
 
-      def required_args
-        arguments_value.filter_map { |arg| arg.name.to_sym if arg.required }
+    def arguments(value = NOT_SET)
+      if value == NOT_SET
+        @arguments_value
+      else
+        @arguments_value = value
       end
     end
+
+    def validate_arguments!(args)
+      missing = required_args - args.keys
+      return if missing.empty?
+
+      raise MCP::Server::RequestHandlerError.new(
+        "Missing required arguments: #{missing.join(", ")}", nil, error_type: :missing_required_arguments
+      )
+    end
+
+    private
+
+    def required_args
+      arguments_value.filter_map { |arg| arg.name.to_sym if arg.required }
+    end
   end
 end

lib/mcp/prompt/argument.rb

@@ -2,7 +2,7 @@
 # frozen_string_literal: true
 
 module MCP
-  class Prompt
+  module Prompt
     class Argument
       attr_reader :name, :description, :required, :arguments
 

lib/mcp/prompt/message.rb

@@ -2,7 +2,7 @@
 # frozen_string_literal: true
 
 module MCP
-  class Prompt
+  module Prompt
     class Message
       attr_reader :role, :content
 

lib/mcp/prompt/result.rb

@@ -2,7 +2,7 @@
 # frozen_string_literal: true
 
 module MCP
-  class Prompt
+  module Prompt
     class Result
       attr_reader :description, :messages
 

lib/mcp/tool.rb

@@ -1,84 +1,85 @@
 # frozen_string_literal: true
 
 module MCP
-  class Tool
-    class << self
-      NOT_SET = Object.new
+  module Tool
+    NOT_SET = Object.new
 
-      attr_reader :description_value
-      attr_reader :input_schema_value
-      attr_reader :annotations_value
+    attr_reader :description_value
+    attr_reader :input_schema_value
+    attr_reader :annotations_value
 
-      def call(*args, server_context:)
-        raise NotImplementedError, "Subclasses must implement call"
+    class << self
+      def define(name: nil, description: nil, input_schema: nil, annotations: nil, &block)
+        Module.new do
+          extend Tool
+          tool_name name
+          description description
+          input_schema input_schema
+          annotations annotations if annotations
+          define_singleton_method(:call, &block) if block
+        end
       end
+    end
 
-      def to_h
-        result = {
-          name: name_value,
-          description: description_value,
-          inputSchema: input_schema_value.to_h,
-        }
-        result[:annotations] = annotations_value.to_h if annotations_value
-        result
-      end
+    def call(*args, server_context:)
+      raise NotImplementedError, "Tools must implement call"
+    end
 
-      def inherited(subclass)
-        super
-        subclass.instance_variable_set(:@name_value, nil)
-        subclass.instance_variable_set(:@description_value, nil)
-        subclass.instance_variable_set(:@input_schema_value, nil)
-        subclass.instance_variable_set(:@annotations_value, nil)
-      end
+    def to_h
+      result = {
+        name: name_value,
+        description: description_value,
+        inputSchema: input_schema_value.to_h,
+      }
+      result[:annotations] = annotations_value.to_h if annotations_value
+      result
+    end
 
-      def tool_name(value = NOT_SET)
-        if value == NOT_SET
-          name_value
-        else
-          @name_value = value
-        end
-      end
+    def extended(mod)
+      super
+      mod.instance_variable_set(:@name_value, nil)
+      mod.instance_variable_set(:@description_value, nil)
+      mod.instance_variable_set(:@input_schema_value, nil)
+      mod.instance_variable_set(:@annotations_value, nil)
+    end
 
-      def name_value
-        @name_value || StringUtils.handle_from_class_name(name)
+    def tool_name(value = NOT_SET)
+      if value == NOT_SET
+        name_value
+      else
+        @name_value = value
       end
+    end
 
-      def description(value = NOT_SET)
-        if value == NOT_SET
-          @description_value
-        else
-          @description_value = value
-        end
-      end
+    def name_value
+      @name_value || StringUtils.handle_from_class_name(name)
+    end
 
-      def input_schema(value = NOT_SET)
-        if value == NOT_SET
-          input_schema_value
-        elsif value.is_a?(Hash)
-          properties = value[:properties] || value["properties"] || {}
-          required = value[:required] || value["required"] || []
-          @input_schema_value = InputSchema.new(properties:, required:)
-        elsif value.is_a?(InputSchema)
-          @input_schema_value = value
-        end
+    def description(value = NOT_SET)
+      if value == NOT_SET
+        @description_value
+      else
+        @description_value = value
       end
+    end
 
-      def annotations(hash = NOT_SET)
-        if hash == NOT_SET
-          @annotations_value
-        else
-          @annotations_value = Annotations.new(**hash)
-        end
+    def input_schema(value = NOT_SET)
+      if value == NOT_SET
+        input_schema_value
+      elsif value.is_a?(Hash)
+        properties = value[:properties] || value["properties"] || {}
+        required = value[:required] || value["required"] || []
+        @input_schema_value = InputSchema.new(properties:, required:)
+      elsif value.is_a?(InputSchema)
+        @input_schema_value = value
       end
+    end
 
-      def define(name: nil, description: nil, input_schema: nil, annotations: nil, &block)
-        Class.new(self) do
-          tool_name name
-          description description
-          input_schema input_schema
-          self.annotations(annotations) if annotations
-          define_singleton_method(:call, &block) if block
-        end
+    def annotations(hash = NOT_SET)
+      if hash == NOT_SET
+        @annotations_value
+      else
+        @annotations_value = Annotations.new(**hash)
       end
     end
   end

lib/mcp/tool/annotations.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 module MCP
-  class Tool
+  module Tool
     class Annotations
       attr_reader :title, :read_only_hint, :destructive_hint, :idempotent_hint, :open_world_hint
 

lib/mcp/tool/input_schema.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 module MCP
-  class Tool
+  module Tool
     class InputSchema
       attr_reader :properties, :required
 

lib/mcp/tool/response.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 module MCP
-  class Tool
+  module Tool
     class Response
       attr_reader :content, :is_error