diff --git a/src/main/java/it/aboutbits/springboot/toolbox/type/CustomType.java b/src/main/java/it/aboutbits/springboot/toolbox/type/CustomType.java
index fd9e12e..130a537 100644
--- a/src/main/java/it/aboutbits/springboot/toolbox/type/CustomType.java
+++ b/src/main/java/it/aboutbits/springboot/toolbox/type/CustomType.java
@@ -1,5 +1,10 @@
 package it.aboutbits.springboot.toolbox.type;
 
+/**
+ * Implementations should override `toString()` by forwarding
+ * the `toString()` method of the wrapped value.
+ * Or return `Objects.toString(value())`
+ */
 public interface CustomType<T> {
     T value();
 }