Support structuredContent in tool response

Author: anandaroop

lib/mcp/tool/response.rb

@@ -5,24 +5,29 @@ class Tool
     class Response
       NOT_GIVEN = Object.new.freeze
 
-      attr_reader :content
+      attr_reader :content, :structured_content
 
-      def initialize(content, deprecated_error = NOT_GIVEN, error: false)
+      def initialize(content = nil, deprecated_error = NOT_GIVEN, error: false, structured_content: 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
         end
 
         @content = content
         @error = error
+
+        if structured_content
+          @structured_content = structured_content
+          @content ||= [{ type: "text", text: structured_content.to_json }]
+        end
       end
 
       def error?
         !!@error
       end
 
       def to_h
-        { content:, isError: error? }.compact
+        { content:, isError: error?, structuredContent: @structured_content }.compact
       end
     end
   end

test/mcp/tool/response_test.rb

@@ -38,6 +38,19 @@ class ResponseTest < ActiveSupport::TestCase
         refute response.error?
       end
 
+      test "#initialize with content and structuredContent" do
+        content = [{
+          type: "text",
+          text: "{\"code\":401,\"message\":\"Unauthorized\"}",
+        }]
+        structured_content = { code: 401, message: "Unauthorized" }
+        response = Response.new(content, structured_content: structured_content)
+
+        assert_equal content, response.content
+        assert_equal structured_content, response.structured_content
+        refute response.error?
+      end
+
       test "#error? for a standard response" do
         response = Response.new(nil, error: false)
         refute response.error?
@@ -72,6 +85,32 @@ class ResponseTest < ActiveSupport::TestCase
         assert_equal content, actual[:content]
         assert actual[:isError]
       end
+
+      test "#to_h for a standard response with content and structured content" do
+        content = [{
+          type: "text",
+          text: "{\"code\":401,\"message\":\"Unauthorized\"}",
+        }]
+        structured_content = { code: 401, message: "Unauthorized" }
+        response = Response.new(content, structured_content: structured_content)
+        actual = response.to_h
+
+        assert_equal [:content, :isError, :structuredContent].sort, actual.keys.sort
+        assert_equal content, actual[:content]
+        assert_equal structured_content, actual[:structuredContent]
+        refute actual[:isError]
+      end
+
+      test "#to_h for a standard response with structured content only" do
+        structured_content = { code: 401, message: "Unauthorized" }
+        response = Response.new(structured_content: structured_content)
+        actual = response.to_h
+
+        assert_equal [:content, :isError, :structuredContent].sort, actual.keys.sort
+        assert_equal [{ type: "text", text: structured_content.to_json }], actual[:content]
+        assert_equal structured_content, actual[:structuredContent]
+        refute actual[:isError]
+      end
     end
   end
 end