Add support for the optional websiteUrl parameter in serverInfo

This PR adds support for the optional `websiteUrl` parameter in `serverInfo`.
This parameter has been supported since the 2025-11-25 MCP specification.

This PR also implements part of #127.

Author: koic

lib/mcp/server.rb

@@ -31,12 +31,13 @@ def initialize(method_name)
 
     include Instrumentation
 
-    attr_accessor :name, :title, :version, :instructions, :tools, :prompts, :resources, :server_context, :configuration, :capabilities, :transport
+    attr_accessor :name, :title, :version, :website_url, :instructions, :tools, :prompts, :resources, :server_context, :configuration, :capabilities, :transport
 
     def initialize(
       name: "model_context_protocol",
       title: nil,
       version: DEFAULT_VERSION,
+      website_url: nil,
       instructions: nil,
       tools: [],
       prompts: [],
@@ -50,6 +51,7 @@ def initialize(
       @name = name
       @title = title
       @version = version
+      @website_url = website_url
       @instructions = instructions
       @tools = tools.to_h { |t| [t.name_value, t] }
       @prompts = prompts.to_h { |p| [p.name_value, p] }
@@ -176,8 +178,8 @@ def prompts_get_handler(&block)
     def validate!
       # NOTE: The draft protocol version is the next version after 2025-03-26.
       if @configuration.protocol_version <= "2025-03-26"
-        if server_info.key?(:title)
-          message = "Error occurred in server_info. `title` is not supported in protocol version 2025-03-26 or earlier"
+        if server_info.key?(:title) || server_info.key?(:websiteUrl)
+          message = "Error occurred in server_info. `title` or `website_url` are not supported in protocol version 2025-03-26 or earlier"
           raise ArgumentError, message
         end
 
@@ -258,6 +260,7 @@ def server_info
         name:,
         title:,
         version:,
+        websiteUrl: website_url,
       }.compact
     end
 

test/mcp/server_test.rb

@@ -779,7 +779,22 @@ def call(message:, server_context: nil)
       assert_equal Configuration::DRAFT_PROTOCOL_VERSION, response[:result][:protocolVersion]
     end
 
-    test "server response does not include title when not configured" do
+    test "server response does not include optionnal parameters when configured" do
+      server = Server.new(title: "Example Server Display Name", name: "test_server", website_url: "https://example.com")
+      request = {
+        jsonrpc: "2.0",
+        method: "initialize",
+        id: 1,
+      }
+
+      response = server.handle(request)
+      server_info = response[:result][:serverInfo]
+
+      assert_equal("Example Server Display Name", server_info[:title])
+      assert_equal("https://example.com", server_info[:websiteUrl])
+    end
+
+    test "server response does not include optionnal parameters when not configured" do
       server = Server.new(name: "test_server")
       request = {
         jsonrpc: "2.0",
@@ -789,6 +804,7 @@ def call(message:, server_context: nil)
 
       response = server.handle(request)
       refute response[:result][:serverInfo].key?(:title)
+      refute response[:result][:serverInfo].key?(:website_url)
     end
 
     test "server uses default version when not configured" do
@@ -858,7 +874,16 @@ def call(message:, server_context: nil)
       exception = assert_raises(ArgumentError) do
         Server.new(name: "test_server", title: "Example Server Display Name", configuration: configuration)
       end
-      assert_equal("Error occurred in server_info. `title` is not supported in protocol version 2025-03-26 or earlier", exception.message)
+      assert_equal("Error occurred in server_info. `title` or `website_url` are not supported in protocol version 2025-03-26 or earlier", exception.message)
+    end
+
+    test "raises error if `website_url` of `server_info` is used with protocol version 2025-03-26" do
+      configuration = Configuration.new(protocol_version: "2025-03-26")
+
+      exception = assert_raises(ArgumentError) do
+        Server.new(name: "test_server", website_url: "https://example.com", configuration: configuration)
+      end
+      assert_equal("Error occurred in server_info. `title` or `website_url` are not supported in protocol version 2025-03-26 or earlier", exception.message)
     end
 
     test "raises error if `title` of tool is used with protocol version 2025-03-26" do