diff --git a/README.md b/README.md
index 94ea866..00c01d8 100644
--- a/README.md
+++ b/README.md
@@ -40,6 +40,8 @@ We have tried to standardize the structure of the actual credential files, as su
   - there is a space after each colon
   - indentation uses four spaces
   - the file ends with a newline character.
+* credentials must use IP:port strings for keys
+  - credentials using hostnames will not be accepted
 
 ```
 {