From 37563e59bd6b2a3022e4d13f0f95db59444ef26e Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Fri, 27 Feb 2026 12:39:16 +0900
Subject: [PATCH] Fix `Content::Image#to_h` to return `mimeType` (camelCase)
 per MCP spec

This is a fix for a similar bug that remained, as in #235.

`Content::Image#to_h` returned `mime_type` (snake_case), but the MCP spec
requires `mimeType` (camelCase) for the MIME type field in image content.
---
 lib/mcp/content.rb       |  2 +-
 test/mcp/content_test.rb | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 test/mcp/content_test.rb

diff --git a/lib/mcp/content.rb b/lib/mcp/content.rb
index 7ab984d6..872de329 100644
--- a/lib/mcp/content.rb
+++ b/lib/mcp/content.rb
@@ -25,7 +25,7 @@ def initialize(data, mime_type, annotations: nil)
       end
 
       def to_h
-        { data: data, mime_type: mime_type, annotations: annotations, type: "image" }.compact
+        { data: data, mimeType: mime_type, annotations: annotations, type: "image" }.compact
       end
     end
   end
diff --git a/test/mcp/content_test.rb b/test/mcp/content_test.rb
new file mode 100644
index 00000000..46ac9021
--- /dev/null
+++ b/test/mcp/content_test.rb
@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+module MCP
+  module Content
+    class ImageTest < ActiveSupport::TestCase
+      test "#to_h returns mimeType (camelCase) per MCP spec" do
+        image = Image.new("base64data", "image/png")
+        result = image.to_h
+
+        assert_equal "image/png", result[:mimeType]
+        refute result.key?(:mime_type), "Expected camelCase mimeType, got snake_case mime_type"
+        assert_equal "image", result[:type]
+        assert_equal "base64data", result[:data]
+      end
+
+      test "#to_h with annotations" do
+        image = Image.new("base64data", "image/png", annotations: { role: "thumbnail" })
+        result = image.to_h
+
+        assert_equal({ role: "thumbnail" }, result[:annotations])
+      end
+
+      test "#to_h without annotations omits the key" do
+        image = Image.new("base64data", "image/png")
+        result = image.to_h
+
+        refute result.key?(:annotations)
+      end
+    end
+  end
+end