diff --git a/types/doc.go b/types/doc.go
new file mode 100644
index 0000000..cc80371
--- /dev/null
+++ b/types/doc.go
@@ -0,0 +1,9 @@
+/*
+Package types provides types to check incoming parameters for validity.
+
+Each type implements the UnmarshalJSON interface, so that it can be fed into
+the Request parser.
+At that time, each error in the parameter is catched and will result in an
+error, so that clients are required to return the correct data.
+*/
+package types
diff --git a/types/zone.go b/types/zone.go
index 1177427..13d0671 100644
--- a/types/zone.go
+++ b/types/zone.go
@@ -6,6 +6,7 @@ import (
 )
 
 type (
+	// Zone represents the name of a zone. A zone must end with a `.`.
 	Zone string
 )