diff --git a/lib/mcp/content.rb b/lib/mcp/content.rb
index 1a1ee03b..591ecb4b 100644
--- a/lib/mcp/content.rb
+++ b/lib/mcp/content.rb
@@ -3,56 +3,60 @@
 module MCP
   module Content
     class Text
-      attr_reader :text, :annotations
+      attr_reader :text, :annotations, :meta
 
-      def initialize(text, annotations: nil)
+      def initialize(text, annotations: nil, meta: nil)
         @text = text
         @annotations = annotations
+        @meta = meta
       end
 
       def to_h
-        { text: text, annotations: annotations, type: "text" }.compact
+        { text: text, annotations: annotations, _meta: meta, type: "text" }.compact
       end
     end
 
     class Image
-      attr_reader :data, :mime_type, :annotations
+      attr_reader :data, :mime_type, :annotations, :meta
 
-      def initialize(data, mime_type, annotations: nil)
+      def initialize(data, mime_type, annotations: nil, meta: nil)
         @data = data
         @mime_type = mime_type
         @annotations = annotations
+        @meta = meta
       end
 
       def to_h
-        { data: data, mimeType: mime_type, annotations: annotations, type: "image" }.compact
+        { data: data, mimeType: mime_type, annotations: annotations, _meta: meta, type: "image" }.compact
       end
     end
 
     class Audio
-      attr_reader :data, :mime_type, :annotations
+      attr_reader :data, :mime_type, :annotations, :meta
 
-      def initialize(data, mime_type, annotations: nil)
+      def initialize(data, mime_type, annotations: nil, meta: nil)
         @data = data
         @mime_type = mime_type
         @annotations = annotations
+        @meta = meta
       end
 
       def to_h
-        { data: data, mimeType: mime_type, annotations: annotations, type: "audio" }.compact
+        { data: data, mimeType: mime_type, annotations: annotations, _meta: meta, type: "audio" }.compact
       end
     end
 
     class EmbeddedResource
-      attr_reader :resource, :annotations
+      attr_reader :resource, :annotations, :meta
 
-      def initialize(resource, annotations: nil)
+      def initialize(resource, annotations: nil, meta: nil)
         @resource = resource
         @annotations = annotations
+        @meta = meta
       end
 
       def to_h
-        { resource: resource.to_h, annotations: annotations, type: "resource" }.compact
+        { resource: resource.to_h, annotations: annotations, _meta: meta, type: "resource" }.compact
       end
     end
   end
diff --git a/lib/mcp/prompt/result.rb b/lib/mcp/prompt/result.rb
index b55b2424..c1fb7404 100644
--- a/lib/mcp/prompt/result.rb
+++ b/lib/mcp/prompt/result.rb
@@ -3,15 +3,16 @@
 module MCP
   class Prompt
     class Result
-      attr_reader :description, :messages
+      attr_reader :description, :messages, :meta
 
-      def initialize(description: nil, messages: [])
+      def initialize(description: nil, messages: [], meta: nil)
         @description = description
         @messages = messages
+        @meta = meta
       end
 
       def to_h
-        { description: description, messages: messages.map(&:to_h) }.compact
+        { description: description, messages: messages.map(&:to_h), _meta: meta }.compact
       end
     end
   end
diff --git a/lib/mcp/resource.rb b/lib/mcp/resource.rb
index 51d92e96..990156b4 100644
--- a/lib/mcp/resource.rb
+++ b/lib/mcp/resource.rb
@@ -5,15 +5,16 @@
 
 module MCP
   class Resource
-    attr_reader :uri, :name, :title, :description, :icons, :mime_type
+    attr_reader :uri, :name, :title, :description, :icons, :mime_type, :meta
 
-    def initialize(uri:, name:, title: nil, description: nil, icons: [], mime_type: nil)
+    def initialize(uri:, name:, title: nil, description: nil, icons: [], mime_type: nil, meta: nil)
       @uri = uri
       @name = name
       @title = title
       @description = description
       @icons = icons
       @mime_type = mime_type
+      @meta = meta
     end
 
     def to_h
@@ -24,6 +25,7 @@ def to_h
         description: description,
         icons: icons&.then { |icons| icons.empty? ? nil : icons.map(&:to_h) },
         mimeType: mime_type,
+        _meta: meta,
       }.compact
     end
   end
diff --git a/lib/mcp/resource/contents.rb b/lib/mcp/resource/contents.rb
index 8322d641..a7569b05 100644
--- a/lib/mcp/resource/contents.rb
+++ b/lib/mcp/resource/contents.rb
@@ -3,23 +3,24 @@
 module MCP
   class Resource
     class Contents
-      attr_reader :uri, :mime_type
+      attr_reader :uri, :mime_type, :meta
 
-      def initialize(uri:, mime_type: nil)
+      def initialize(uri:, mime_type: nil, meta: nil)
         @uri = uri
         @mime_type = mime_type
+        @meta = meta
       end
 
       def to_h
-        { uri: uri, mimeType: mime_type }.compact
+        { uri: uri, mimeType: mime_type, _meta: meta }.compact
       end
     end
 
     class TextContents < Contents
       attr_reader :text
 
-      def initialize(text:, uri:, mime_type:)
-        super(uri: uri, mime_type: mime_type)
+      def initialize(text:, uri:, mime_type:, meta: nil)
+        super(uri: uri, mime_type: mime_type, meta: meta)
         @text = text
       end
 
@@ -31,8 +32,8 @@ def to_h
     class BlobContents < Contents
       attr_reader :data
 
-      def initialize(data:, uri:, mime_type:)
-        super(uri: uri, mime_type: mime_type)
+      def initialize(data:, uri:, mime_type:, meta: nil)
+        super(uri: uri, mime_type: mime_type, meta: meta)
         @data = data
       end
 
diff --git a/lib/mcp/resource_template.rb b/lib/mcp/resource_template.rb
index 871600e8..b23ecd01 100644
--- a/lib/mcp/resource_template.rb
+++ b/lib/mcp/resource_template.rb
@@ -2,15 +2,16 @@
 
 module MCP
   class ResourceTemplate
-    attr_reader :uri_template, :name, :title, :description, :icons, :mime_type
+    attr_reader :uri_template, :name, :title, :description, :icons, :mime_type, :meta
 
-    def initialize(uri_template:, name:, title: nil, description: nil, icons: [], mime_type: nil)
+    def initialize(uri_template:, name:, title: nil, description: nil, icons: [], mime_type: nil, meta: nil)
       @uri_template = uri_template
       @name = name
       @title = title
       @description = description
       @icons = icons
       @mime_type = mime_type
+      @meta = meta
     end
 
     def to_h
@@ -21,6 +22,7 @@ def to_h
         description: description,
         icons: icons&.then { |icons| icons.empty? ? nil : icons.map(&:to_h) },
         mimeType: mime_type,
+        _meta: meta,
       }.compact
     end
   end
diff --git a/lib/mcp/tool/response.rb b/lib/mcp/tool/response.rb
index 0d9dccbb..2532ea83 100644
--- a/lib/mcp/tool/response.rb
+++ b/lib/mcp/tool/response.rb
@@ -5,9 +5,9 @@ class Tool
     class Response
       NOT_GIVEN = Object.new.freeze
 
-      attr_reader :content, :structured_content
+      attr_reader :content, :structured_content, :meta
 
-      def initialize(content = nil, deprecated_error = NOT_GIVEN, error: false, structured_content: nil)
+      def initialize(content = nil, deprecated_error = NOT_GIVEN, error: false, structured_content: nil, meta: nil)
         if deprecated_error != NOT_GIVEN
           warn("Passing `error` with the 2nd argument of `Response.new` is deprecated. Use keyword argument like `Response.new(content, error: error)` instead.", uplevel: 1)
           error = deprecated_error
@@ -16,6 +16,7 @@ def initialize(content = nil, deprecated_error = NOT_GIVEN, error: false, struct
         @content = content || []
         @error = error
         @structured_content = structured_content
+        @meta = meta
       end
 
       def error?
@@ -23,7 +24,7 @@ def error?
       end
 
       def to_h
-        { content: content, isError: error?, structuredContent: @structured_content }.compact
+        { content: content, isError: error?, structuredContent: @structured_content, _meta: meta }.compact
       end
     end
   end
diff --git a/test/mcp/content_test.rb b/test/mcp/content_test.rb
index f2f5cad2..fc2103ee 100644
--- a/test/mcp/content_test.rb
+++ b/test/mcp/content_test.rb
@@ -28,6 +28,19 @@ class ImageTest < ActiveSupport::TestCase
 
         refute result.key?(:annotations)
       end
+
+      test "#to_h with meta" do
+        meta = { "application/vnd.ant.mcp-app" => { "csp" => "default-src 'self'" } }
+        image = Image.new("base64data", "image/png", meta: meta)
+
+        assert_equal meta, image.to_h[:_meta]
+      end
+
+      test "#to_h without meta omits the key" do
+        image = Image.new("base64data", "image/png")
+
+        refute image.to_h.key?(:_meta)
+      end
     end
 
     class AudioTest < ActiveSupport::TestCase
@@ -53,6 +66,19 @@ class AudioTest < ActiveSupport::TestCase
 
         refute result.key?(:annotations)
       end
+
+      test "#to_h with meta" do
+        meta = { "application/vnd.ant.mcp-app" => { "csp" => "default-src 'self'" } }
+        audio = Audio.new("base64data", "audio/wav", meta: meta)
+
+        assert_equal meta, audio.to_h[:_meta]
+      end
+
+      test "#to_h without meta omits the key" do
+        audio = Audio.new("base64data", "audio/wav")
+
+        refute audio.to_h.key?(:_meta)
+      end
     end
 
     class EmbeddedResourceTest < ActiveSupport::TestCase
@@ -92,6 +118,52 @@ def resource.to_h
 
         refute result.key?(:annotations)
       end
+
+      test "#to_h with meta" do
+        resource = Object.new
+        def resource.to_h
+          { uri: "test://x" }
+        end
+
+        meta = { "application/vnd.ant.mcp-app" => { "csp" => "default-src 'self'" } }
+        embedded = EmbeddedResource.new(resource, meta: meta)
+
+        assert_equal meta, embedded.to_h[:_meta]
+      end
+
+      test "#to_h without meta omits the key" do
+        resource = Object.new
+        def resource.to_h
+          { uri: "test://x" }
+        end
+
+        embedded = EmbeddedResource.new(resource)
+
+        refute embedded.to_h.key?(:_meta)
+      end
+    end
+
+    class TextTest < ActiveSupport::TestCase
+      test "#to_h returns correct format per MCP spec" do
+        text = Text.new("hello")
+        result = text.to_h
+
+        assert_equal "text", result[:type]
+        assert_equal "hello", result[:text]
+      end
+
+      test "#to_h with meta" do
+        meta = { "application/vnd.ant.mcp-app" => { "csp" => "default-src 'self'" } }
+        text = Text.new("hello", meta: meta)
+
+        assert_equal meta, text.to_h[:_meta]
+      end
+
+      test "#to_h without meta omits the key" do
+        text = Text.new("hello")
+
+        refute text.to_h.key?(:_meta)
+      end
     end
   end
 end
diff --git a/test/mcp/prompt/result_test.rb b/test/mcp/prompt/result_test.rb
new file mode 100644
index 00000000..62f161e2
--- /dev/null
+++ b/test/mcp/prompt/result_test.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+module MCP
+  class Prompt
+    class ResultTest < ActiveSupport::TestCase
+      test "#to_h returns description and messages" do
+        result = Prompt::Result.new(
+          description: "a prompt",
+          messages: [Prompt::Message.new(role: "user", content: Content::Text.new("hi"))],
+        )
+
+        hash = result.to_h
+
+        assert_equal "a prompt", hash[:description]
+        assert_equal 1, hash[:messages].size
+      end
+
+      test "#to_h includes _meta when present" do
+        meta = { "application/vnd.ant.mcp-app" => { "csp" => "default-src 'self'" } }
+        result = Prompt::Result.new(
+          description: "a prompt",
+          messages: [Prompt::Message.new(role: "user", content: Content::Text.new("hi"))],
+          meta: meta,
+        )
+
+        assert_equal meta, result.to_h[:_meta]
+      end
+
+      test "#to_h omits _meta when nil" do
+        result = Prompt::Result.new(
+          description: "a prompt",
+          messages: [Prompt::Message.new(role: "user", content: Content::Text.new("hi"))],
+        )
+
+        refute result.to_h.key?(:_meta)
+      end
+    end
+  end
+end
diff --git a/test/mcp/resource/contents_test.rb b/test/mcp/resource/contents_test.rb
index 53efaa6a..f89f8f22 100644
--- a/test/mcp/resource/contents_test.rb
+++ b/test/mcp/resource/contents_test.rb
@@ -70,6 +70,78 @@ class ContentsTest < ActiveSupport::TestCase
         assert_equal({ uri: "test://binary", blob: "base64data" }, result)
         refute result.key?(:mimeType)
       end
+
+      test "Contents#to_h omits _meta when nil" do
+        contents = Resource::Contents.new(uri: "test://example", mime_type: "text/plain")
+
+        refute contents.to_h.key?(:_meta)
+      end
+
+      test "Contents#to_h includes _meta when present" do
+        meta = { "application/vnd.ant.mcp-app" => { "csp" => "default-src 'self'" } }
+        contents = Resource::Contents.new(uri: "test://example", mime_type: "text/plain", meta: meta)
+
+        assert_equal meta, contents.to_h[:_meta]
+      end
+
+      test "TextContents#to_h includes _meta when present" do
+        meta = { "application/vnd.ant.mcp-app" => { "csp" => "default-src 'self'" } }
+        text_contents = Resource::TextContents.new(
+          uri: "test://text",
+          mime_type: "text/plain",
+          text: "Hello",
+          meta: meta,
+        )
+
+        result = text_contents.to_h
+
+        assert_equal meta, result[:_meta]
+        assert_equal "Hello", result[:text]
+      end
+
+      test "TextContents#to_h omits _meta when nil" do
+        text_contents = Resource::TextContents.new(
+          uri: "test://text",
+          mime_type: "text/plain",
+          text: "Hello",
+        )
+
+        refute text_contents.to_h.key?(:_meta)
+      end
+
+      test "BlobContents#to_h includes _meta when present" do
+        meta = { "application/vnd.ant.mcp-app" => { "csp" => "default-src 'self'" } }
+        blob_contents = Resource::BlobContents.new(
+          uri: "test://binary",
+          mime_type: "image/png",
+          data: "base64data",
+          meta: meta,
+        )
+
+        result = blob_contents.to_h
+
+        assert_equal meta, result[:_meta]
+        assert_equal "base64data", result[:blob]
+      end
+
+      test "BlobContents#to_h omits _meta when nil" do
+        blob_contents = Resource::BlobContents.new(
+          uri: "test://binary",
+          mime_type: "image/png",
+          data: "base64data",
+        )
+
+        refute blob_contents.to_h.key?(:_meta)
+      end
+
+      test "Contents#to_h preserves empty _meta hash" do
+        contents = Resource::Contents.new(uri: "test://example", mime_type: "text/plain", meta: {})
+
+        result = contents.to_h
+
+        assert result.key?(:_meta)
+        assert_equal({}, result[:_meta])
+      end
     end
   end
 end
diff --git a/test/mcp/resource_template_test.rb b/test/mcp/resource_template_test.rb
index 6b8a565e..8d25be04 100644
--- a/test/mcp/resource_template_test.rb
+++ b/test/mcp/resource_template_test.rb
@@ -36,5 +36,22 @@ class ResourceTemplateTest < ActiveSupport::TestCase
 
       assert_equal expected_icons, resource_template.to_h[:icons]
     end
+
+    test "#to_h omits _meta when nil" do
+      resource_template = ResourceTemplate.new(uri_template: "file:///{path}", name: "template_without_meta")
+
+      refute resource_template.to_h.key?(:_meta)
+    end
+
+    test "#to_h includes _meta when present" do
+      meta = { "application/vnd.ant.mcp-app" => { "csp" => "default-src 'self'" } }
+      resource_template = ResourceTemplate.new(
+        uri_template: "file:///{path}",
+        name: "template_with_meta",
+        meta: meta,
+      )
+
+      assert_equal meta, resource_template.to_h[:_meta]
+    end
   end
 end
diff --git a/test/mcp/resource_test.rb b/test/mcp/resource_test.rb
index 9e780120..fb2254d4 100644
--- a/test/mcp/resource_test.rb
+++ b/test/mcp/resource_test.rb
@@ -36,5 +36,18 @@ class ResourceTest < ActiveSupport::TestCase
 
       assert_equal expected_icons, resource.to_h[:icons]
     end
+
+    test "#to_h omits _meta when nil" do
+      resource = Resource.new(uri: "file:///test.txt", name: "resource_without_meta")
+
+      refute resource.to_h.key?(:_meta)
+    end
+
+    test "#to_h includes _meta when present" do
+      meta = { "application/vnd.ant.mcp-app" => { "csp" => "default-src 'self'" } }
+      resource = Resource.new(uri: "file:///test.txt", name: "resource_with_meta", meta: meta)
+
+      assert_equal meta, resource.to_h[:_meta]
+    end
   end
 end
diff --git a/test/mcp/tool/response_test.rb b/test/mcp/tool/response_test.rb
index 6277e18b..122dbb07 100644
--- a/test/mcp/tool/response_test.rb
+++ b/test/mcp/tool/response_test.rb
@@ -122,6 +122,20 @@ class ResponseTest < ActiveSupport::TestCase
         assert_equal structured_content, actual[:structuredContent]
         refute actual[:isError]
       end
+
+      test "#to_h includes _meta when present" do
+        meta = { "application/vnd.ant.mcp-app" => { "csp" => "default-src 'self'" } }
+        response = Response.new([{ type: "text", text: "ok" }], meta: meta)
+        actual = response.to_h
+
+        assert_equal meta, actual[:_meta]
+      end
+
+      test "#to_h omits _meta when nil" do
+        response = Response.new([{ type: "text", text: "ok" }])
+
+        refute response.to_h.key?(:_meta)
+      end
     end
   end
 end