diff --git a/README.md b/README.md
index 0a3ab8e9f..84f5b883e 100644
--- a/README.md
+++ b/README.md
@@ -123,6 +123,10 @@ main:
 <USERNAME> <SPACE> <PASSWORD> <SPACE> <MARK> <LF>
 ```
 
+- USERNAME: A string of up to 255 characters
+- PASSWORD: A string of up to 255 characters
+- MARK: Hexadecimal
+
 ### Run
 
 ```bash