diff --git a/validation.md b/validation.md
index 00129ea224f..ec19f18787b 100644
--- a/validation.md
+++ b/validation.md
@@ -846,6 +846,7 @@ Below is a list of all available validation rules and their function:
 [JSON](#rule-json)
 [Less Than](#rule-lt)
 [Less Than Or Equal](#rule-lte)
+[Lowercase](#rule-lowercase)
 [MAC Address](#rule-mac)
 [Max](#rule-max)
 [Max Digits](#rule-max-digits)
@@ -1315,6 +1316,11 @@ The field under validation must be less than the given _field_. The two fields m
 
 The field under validation must be less than or equal to the given _field_. The two fields must be of the same type. Strings, numerics, arrays, and files are evaluated using the same conventions as the [`size`](#rule-size) rule.
 
+<a name="rule-lowercase"></a>
+#### lowercase:_field_
+
+The field under validation must be lowercase.
+
 <a name="rule-mac"></a>
 #### mac_address