diff --git a/README.md b/README.md
new file mode 100644
index 0000000..b300d55
--- /dev/null
+++ b/README.md
@@ -0,0 +1,13 @@
+# check_nmap.sh
+This script runs a nmap scan and checks the discovered ports against a whitelist
+
+## Arguments
+* --host  | -h: Host that shall be scanned by nmap
+* --portrange | -p: Ports that shall be scanned (nmap format)
+* --known | -k: A port number that is expected to be open
+* --input | -i: Use input file instead of a real nmap scan (for testing)
+* --debug | -d: More debugging output, cannot be used with icinga2
+* all arguments after -- are passed to nmap
+
+## Results
+* CRITICAL: if any expected port is open