Merge pull request #190 from koic/avoid_draft_protocol_version

Default to the latest stable protocol version

Author: koic

README.md

@@ -349,7 +349,8 @@ configuration = MCP::Configuration.new(protocol_version: "2024-11-05")
 MCP::Server.new(name: "test_server", configuration: configuration)
 ```
 
-If no protocol version is specified, the [Draft version](https://modelcontextprotocol.io/specification/draft) will be applied by default.
+If no protocol version is specified, the latest stable version will be applied by default.
+The latest stable version includes new features from the [draft version](https://modelcontextprotocol.io/specification/draft).
 
 This will make all new server instances use the specified protocol version instead of the default version. The protocol version can be reset to the default by setting it to `nil`:
 

lib/mcp/configuration.rb

@@ -2,10 +2,8 @@
 
 module MCP
   class Configuration
-    # DRAFT-2025-v3 is the latest draft protocol version:
-    # https://github.com/modelcontextprotocol/modelcontextprotocol/blob/14ec41c/schema/draft/schema.ts#L15
-    DRAFT_PROTOCOL_VERSION = "DRAFT-2025-v3"
-    SUPPORTED_STABLE_PROTOCOL_VERSIONS = ["2025-06-18", "2025-03-26", "2024-11-05"]
+    LATEST_STABLE_PROTOCOL_VERSION = "2025-06-18"
+    SUPPORTED_STABLE_PROTOCOL_VERSIONS = [LATEST_STABLE_PROTOCOL_VERSION, "2025-03-26", "2024-11-05"]
 
     attr_writer :exception_reporter, :instrumentation_callback
 
@@ -35,7 +33,7 @@ def validate_tool_call_arguments=(validate_tool_call_arguments)
     end
 
     def protocol_version
-      @protocol_version || DRAFT_PROTOCOL_VERSION
+      @protocol_version || LATEST_STABLE_PROTOCOL_VERSION
     end
 
     def protocol_version?

test/mcp/configuration_test.rb

@@ -38,18 +38,19 @@ class ConfigurationTest < ActiveSupport::TestCase
     # https://github.com/modelcontextprotocol/modelcontextprotocol/blob/14ec41c/schema/draft/schema.ts#L15
     test "initializes with default protocol version" do
       config = Configuration.new
-      assert_equal Configuration::DRAFT_PROTOCOL_VERSION, config.protocol_version
+      assert_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, config.protocol_version
     end
 
     test "uses the draft protocol version when protocol_version is set to nil" do
       config = Configuration.new(protocol_version: nil)
-      assert_equal Configuration::DRAFT_PROTOCOL_VERSION, config.protocol_version
+      assert_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, config.protocol_version
     end
 
     test "raises ArgumentError when setting the draft protocol version" do
       exception = assert_raises(ArgumentError) do
-        # To use the draft version externally, either omit `protocol_version` or set it to nil.
-        Configuration.new(protocol_version: Configuration::DRAFT_PROTOCOL_VERSION)
+        # DRAFT-2025-v3 is the latest draft protocol version:
+        # https://github.com/modelcontextprotocol/modelcontextprotocol/blob/14ec41c/schema/draft/schema.ts#L15
+        Configuration.new(protocol_version: "DRAFT-2025-v3")
       end
 
       assert_equal("protocol_version must be 2025-06-18, 2025-03-26, or 2024-11-05", exception.message)

test/mcp/server/transports/streamable_http_transport_test.rb

@@ -81,7 +81,7 @@ class StreamableHTTPTransportTest < ActiveSupport::TestCase
           body = JSON.parse(response[2][0])
           assert_equal "2.0", body["jsonrpc"]
           assert_equal "123", body["id"]
-          assert_equal Configuration::DRAFT_PROTOCOL_VERSION, body["result"]["protocolVersion"]
+          assert_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, body["result"]["protocolVersion"]
         end
 
         test "handles GET request with valid session ID" do

test/mcp/server_test.rb

@@ -133,7 +133,7 @@ class ServerTest < ActiveSupport::TestCase
         jsonrpc: "2.0",
         id: 1,
         result: {
-          protocolVersion: Configuration::DRAFT_PROTOCOL_VERSION,
+          protocolVersion: Configuration::LATEST_STABLE_PROTOCOL_VERSION,
           capabilities: {
             prompts: { listChanged: true },
             resources: { listChanged: true },
@@ -776,7 +776,7 @@ def call(message:, server_context: nil)
       }
 
       response = @server.handle(request)
-      assert_equal Configuration::DRAFT_PROTOCOL_VERSION, response[:result][:protocolVersion]
+      assert_equal Configuration::LATEST_STABLE_PROTOCOL_VERSION, response[:result][:protocolVersion]
     end
 
     test "server response does not include title when not configured" do