diff --git a/annotation.go b/annotation.go
index c634f47..e01c75f 100644
--- a/annotation.go
+++ b/annotation.go
@@ -7,8 +7,9 @@ import (
 const (
 	AnnotationTag = "annotation"
 
-	NameTag    = "@name"
-	DefaultTag = "@default"
+	NameTag     = "@name"
+	DefaultTag  = "@default"
+	RequiredTag = "@required"
 )
 
 var (