diff --git a/welcome_mail.api.php b/welcome_mail.api.php
new file mode 100644
index 0000000..4b15449
--- /dev/null
+++ b/welcome_mail.api.php
@@ -0,0 +1,30 @@
+<?php
+
+/**
+ * @file
+ * Welcome Mail API file.
+ */
+
+/**
+ * @addtogroup hooks
+ * @{
+ */
+
+/**
+ * Declaration of hook_welcome_mail_mail_alter().
+ *
+ * Let other modules alter the default message to be sent through welcome_mail
+ * module. This will override its behavior via hook_welcome_mail_mail_alter().
+ *
+ * @param array $message
+ *   An array with keys 'id', 'to', 'subject', 'body', 'from', 'headers', like
+ *   in hook_mail(). Link to Drupal API follows:
+ *   https://api.drupal.org/api/drupal/core%21core.api.php/function/hook_mail/.
+ */
+function hook_welcome_mail_mail_alter(array &$message) {
+  return $message;
+}
+
+/**
+ * @} End of "addtogroup hooks".
+ */