Merge pull request #153 from modelcontextprotocol/prompt-spec-compliance

fix `Prompt` type gaps with 2025-06-18 spec

Author: koic

README.md

@@ -623,10 +623,12 @@ class MyPrompt < MCP::Prompt
   arguments [
     MCP::Prompt::Argument.new(
       name: "message",
+      title: "Message Title",
       description: "Input message",
       required: true
     )
   ]
+  meta({ version: "1.0", category: "example" })
 
   class << self
     def template(args, server_context:)
@@ -660,10 +662,12 @@ prompt = MCP::Prompt.define(
   arguments: [
     MCP::Prompt::Argument.new(
       name: "message",
+      title: "Message Title",
       description: "Input message",
       required: true
     )
-  ]
+  ],
+  meta: { version: "1.0", category: "example" }
 ) do |args, server_context:|
   MCP::Prompt::Result.new(
     description: "Response description",
@@ -691,10 +695,12 @@ server.define_prompt(
   arguments: [
     Prompt::Argument.new(
       name: "message",
+      title: "Message Title",
       description: "Input message",
       required: true
     )
-  ]
+  ],
+  meta: { version: "1.0", category: "example" }
 ) do |args, server_context:|
   Prompt::Result.new(
     description: "Response description",
@@ -717,7 +723,7 @@ e.g. around authentication state or user preferences.
 
 ### Key Components
 
-- `MCP::Prompt::Argument` - Defines input parameters for the prompt template
+- `MCP::Prompt::Argument` - Defines input parameters for the prompt template with name, title, description, and required flag
 - `MCP::Prompt::Message` - Represents a message in the conversation with a role and content
 - `MCP::Prompt::Result` - The output of a prompt template containing description and messages
 - `MCP::Content::Text` - Text content for messages

lib/mcp/prompt.rb

@@ -8,13 +8,20 @@ class << self
       attr_reader :title_value
       attr_reader :description_value
       attr_reader :arguments_value
+      attr_reader :meta_value
 
       def template(args, server_context: nil)
         raise NotImplementedError, "Subclasses must implement template"
       end
 
       def to_h
-        { name: name_value, title: title_value, description: description_value, arguments: arguments_value.map(&:to_h) }.compact
+        {
+          name: name_value,
+          title: title_value,
+          description: description_value,
+          arguments: arguments_value&.map(&:to_h),
+          _meta: meta_value,
+        }.compact
       end
 
       def inherited(subclass)
@@ -23,6 +30,7 @@ def inherited(subclass)
         subclass.instance_variable_set(:@title_value, nil)
         subclass.instance_variable_set(:@description_value, nil)
         subclass.instance_variable_set(:@arguments_value, nil)
+        subclass.instance_variable_set(:@meta_value, nil)
       end
 
       def prompt_name(value = NOT_SET)
@@ -61,7 +69,15 @@ def arguments(value = NOT_SET)
         end
       end
 
-      def define(name: nil, title: nil, description: nil, arguments: [], &block)
+      def meta(value = NOT_SET)
+        if value == NOT_SET
+          @meta_value
+        else
+          @meta_value = value
+        end
+      end
+
+      def define(name: nil, title: nil, description: nil, arguments: [], meta: nil, &block)
         Class.new(self) do
           prompt_name name
           title title
@@ -70,6 +86,7 @@ def define(name: nil, title: nil, description: nil, arguments: [], &block)
           define_singleton_method(:template) do |args, server_context: nil|
             instance_exec(args, server_context:, &block)
           end
+          meta meta
         end
       end
 

lib/mcp/prompt/argument.rb

@@ -3,17 +3,22 @@
 module MCP
   class Prompt
     class Argument
-      attr_reader :name, :description, :required, :arguments
+      attr_reader :name, :title, :description, :required
 
-      def initialize(name:, description: nil, required: false)
+      def initialize(name:, title: nil, description: nil, required: false)
         @name = name
+        @title = title
         @description = description
         @required = required
-        @arguments = arguments
       end
 
       def to_h
-        { name:, description:, required: }.compact
+        {
+          name: name,
+          title: title,
+          description: description,
+          required: required,
+        }.compact
       end
     end
   end

test/mcp/prompt_test.rb

@@ -113,8 +113,14 @@ def template(args, server_context:)
         title: "Mock Prompt",
         description: "a mock prompt for testing",
         arguments: [
-          Prompt::Argument.new(name: "test_argument", description: "Test argument", required: true),
+          Prompt::Argument.new(
+            name: "test_argument",
+            title: "Test argument title",
+            description: "This is a test argument description",
+            required: true,
+          ),
         ],
+        meta: { foo: "bar" },
       ) do |args, server_context:|
         content = Content::Text.new(args["test_argument"] + " user: #{server_context[:user_id]}")
 
@@ -130,6 +136,10 @@ def template(args, server_context:)
       assert_equal "mock_prompt", prompt.name_value
       assert_equal "a mock prompt for testing", prompt.description
       assert_equal "test_argument", prompt.arguments.first.name
+      assert_equal "Test argument title", prompt.arguments.first.title
+      assert_equal "This is a test argument description", prompt.arguments.first.description
+      assert prompt.arguments.first.required
+      assert_equal({ foo: "bar" }, prompt.meta_value)
 
       expected = {
         description: "Hello, world!",
@@ -142,5 +152,43 @@ def template(args, server_context:)
       result = prompt.template({ "test_argument" => "Hello, friend!" }, server_context: { user_id: 123 })
       assert_equal expected, result.to_h
     end
+
+    test "#to_h returns a hash with name, title, description, arguments, and meta" do
+      class FullPrompt < Prompt
+        prompt_name "test_prompt"
+        description "Test prompt description"
+        title "Test Prompt title"
+        arguments [
+          Prompt::Argument.new(name: "test_argument", description: "Test argument", required: true),
+        ]
+        meta({ test: "meta" })
+      end
+
+      expected = {
+        name: "test_prompt",
+        title: "Test Prompt title",
+        description: "Test prompt description",
+        arguments: [
+          { name: "test_argument", description: "Test argument", required: true },
+        ],
+        _meta: { test: "meta" },
+      }
+
+      assert_equal expected, FullPrompt.to_h
+    end
+
+    test "#to_h handles nil arguments value" do
+      class NoArgumentsPrompt < Prompt
+        description "No arguments prompt"
+      end
+      prompt = NoArgumentsPrompt
+
+      expected = {
+        name: "no_arguments_prompt",
+        description: "No arguments prompt",
+      }
+
+      assert_equal expected, prompt.to_h
+    end
   end
 end