add _meta field to Prompt

> See [General fields: `_meta`](/specification/2025-06-18/basic/index#meta) for notes on `_meta` usage.

51e093b8eb/schema/2025-06-18/schema.ts (L680-L683)

README.md

@@ -629,6 +629,7 @@ class MyPrompt < MCP::Prompt
       required: true
     )
   ]
+  meta({ version: "1.0", category: "example" })
 
   class << self
     def template(args, server_context:)
@@ -666,7 +667,8 @@ prompt = MCP::Prompt.define(
       description: "Input message",
       required: true
     )
-  ]
+  ],
+  meta: { version: "1.0", category: "example" }
 ) do |args, server_context:|
   MCP::Prompt::Result.new(
     description: "Response description",
@@ -698,7 +700,8 @@ server.define_prompt(
       description: "Input message",
       required: true
     )
-  ]
+  ],
+  meta: { version: "1.0", category: "example" }
 ) do |args, server_context:|
   Prompt::Result.new(
     description: "Response description",

lib/mcp/prompt.rb

@@ -8,13 +8,20 @@ module MCP
       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 @@ module MCP
         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 @@ module MCP
         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 @@ module MCP
           define_singleton_method(:template) do |args, server_context: nil|
             instance_exec(args, server_context:, &block)
           end
+          meta meta
         end
       end
 

test/mcp/prompt_test.rb

@@ -120,6 +120,7 @@ module MCP
             required: true,
           ),
         ],
+        meta: { foo: "bar" },
       ) do |args, server_context:|
         content = Content::Text.new(args["test_argument"] + " user: #{server_context[:user_id]}")
 
@@ -135,6 +136,10 @@ module MCP
       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!",
@@ -147,5 +152,43 @@ module MCP
       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