diff --git a/README.md b/README.md
index ec4e798..f72355f 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,12 @@
 
 Monitoring plugin to check if containers are upgradable. By default all running container are checked.
 
-Check are done by running Icinga/Nagios compatible check plugin inside containers.
+Checks are done by running Icinga/Nagios compatible check plugins inside containers. These plugins are listed inside the `CHECK_PLUGINS` associative array (on top of the file) and by default, the following plugin are declared:
+
+- `/usr/lib/nagios/plugins/check_apt`: for Debian based image, provide by the `monitoring-plugins-basic` debian package
+- `/usr/lib/nagios/plugins/check_apk`: for Alpine based image, see [project](https://gitea.zionetrix.net/bn8/check_apk) for install instructions
+
+__Note:__ The first plugin detected as installed will be used.
 
 ## Installation