diff --git a/src/main/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt b/src/main/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt
index 1bb5e3e..ae361be 100644
--- a/src/main/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt
+++ b/src/main/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt
@@ -1003,6 +1003,7 @@ public data class Tool(
     @Serializable
     public data class Input(
         val properties: JsonObject = EmptyJsonObject,
+        val required: List<String>? = null,
     ) {
         val type: String = "object"
     }