diff --git a/Validation-Configuration.md b/Validation-Configuration.md
index 658aa1a..22d9483 100644
--- a/Validation-Configuration.md
+++ b/Validation-Configuration.md
@@ -95,6 +95,12 @@ _(Empty cells are not checked, see not empty validation)_
 The value can only be numerics and alphabetic characters.
 _(Empty cells are not checked, see not empty validation)_
 
+### unique
+
+	"unique" : true
+
+The value can only exist once in this column.
+
 ### regexp
 
 	"regexp" : "[0-9a-zA-Z]*"