diff --git a/README.md b/README.md
index 8dad241..0cbd174 100644
--- a/README.md
+++ b/README.md
@@ -44,13 +44,16 @@ void main() async {
   server.tool(
     "calculate",
     description: 'Perform basic arithmetic operations',
-    inputSchemaProperties: {
-      'operation': {
-        'type': 'string',
-        'enum': ['add', 'subtract', 'multiply', 'divide'],
+    inputSchema: {
+      'properties': {
+        'operation': {
+          'type': 'string',
+          'enum': ['add', 'subtract', 'multiply', 'divide'],
+        },
+        'a': {'type': 'number'},
+        'b': {'type': 'number'},
       },
-      'a': {'type': 'number'},
-      'b': {'type': 'number'},
+      'required': ['operation', 'a', 'b'],
     },
     callback: ({args, extra}) async {
       final operation = args!['operation'];
diff --git a/lib/src/server/mcp.dart b/lib/src/server/mcp.dart
index 8dd2157..a59fd40 100644
--- a/lib/src/server/mcp.dart
+++ b/lib/src/server/mcp.dart
@@ -82,17 +82,17 @@ class ResourceTemplateRegistration {
 
 class _RegisteredTool {
   final String? description;
-  final Map<String, dynamic>? inputSchemaProperties;
+  final Map<String, dynamic>? inputSchema;
   final ToolCallback callback;
 
   const _RegisteredTool({
     this.description,
-    this.inputSchemaProperties,
+    this.inputSchema,
     required this.callback,
   });
 
   Tool toTool(String name) {
-    final schema = ToolInputSchema(properties: inputSchemaProperties);
+    final schema = ToolInputSchema.fromJson(inputSchema ?? {});
     return Tool(name: name, description: description, inputSchema: schema);
   }
 }
@@ -561,7 +561,7 @@ class McpServer {
   void tool(
     String name, {
     String? description,
-    Map<String, dynamic>? inputSchemaProperties,
+    Map<String, dynamic>? inputSchema,
     required ToolCallback callback,
   }) {
     if (_registeredTools.containsKey(name)) {
@@ -569,7 +569,7 @@ class McpServer {
     }
     _registeredTools[name] = _RegisteredTool(
       description: description,
-      inputSchemaProperties: inputSchemaProperties,
+      inputSchema: inputSchema,
       callback: callback,
     );
     _ensureToolHandlersInitialized();
diff --git a/lib/src/types.dart b/lib/src/types.dart
index 952d445..f2dd2d3 100644
--- a/lib/src/types.dart
+++ b/lib/src/types.dart
@@ -1756,26 +1756,36 @@ class JsonRpcPromptListChangedNotification extends JsonRpcNotification {
 
 /// Describes the input schema for a tool, based on JSON Schema.
 class ToolInputSchema {
-  /// Must be "object".
-  final String type = "object";
+  /// Must be "object" at the top level.
+  final String type;
 
   /// JSON Schema properties definition.
-  final Map<String, dynamic>? properties;
+  final ToolInputSchema? properties;
+
+  /// Optional list of required properties.
+  final List<String>? required;
 
-  /// Additional JSON Schema properties (e.g., required).
+  /// Additional JSON Schema properties.
   final Map<String, dynamic> additionalProperties;
 
   const ToolInputSchema({
+    required this.type,
     this.properties,
+    this.required,
     this.additionalProperties = const {},
   });
 
   factory ToolInputSchema.fromJson(Map<String, dynamic> json) {
     final rest = Map<String, dynamic>.from(json)
       ..remove('type')
-      ..remove('properties');
+      ..remove('properties')
+      ..remove('required');
     return ToolInputSchema(
-      properties: json['properties'] as Map<String, dynamic>?,
+      type: json['type'] ?? "object",
+      properties: json['properties'] != null
+          ? ToolInputSchema.fromJson(json['properties'])
+          : null,
+      required: (json['required'] as List<dynamic>?)?.cast<String>(),
       additionalProperties: rest,
     );
   }
@@ -1783,6 +1793,7 @@ class ToolInputSchema {
   Map<String, dynamic> toJson() => {
         'type': type,
         if (properties != null) 'properties': properties,
+        if (required != null) 'required': required,
         ...additionalProperties,
       };
 }