diff --git a/README.md b/README.md
index 5685834..0208e72 100644
--- a/README.md
+++ b/README.md
@@ -25,3 +25,17 @@ To install tinystatus:
 * Generate status page `./tinystatus > index.html`
 * Serve the page with your favorite web server
 
+## Configuration file
+
+The syntax of `checks.list` file is:
+```
+Command | Expected Code | Status Text | Host to check
+```
+
+Command can be:
+* `http` - Check http status
+* `ping` - Check ping status 
+* `port` - Check open port status
+
+There are also `http4`, `http6`, `ping4`, `ping6`, `port4`, `port6` for IPv4 or IPv6 only check.
+
diff --git a/checks.list b/checks.list
index 07a1543..7375b0b 100644
--- a/checks.list
+++ b/checks.list
@@ -1,4 +1,6 @@
-http | 200 | Google website      | https://google.com
-http | 404 | Google 404          | https://google.com/dummy
-ping | 0   | Google ping         | 8.8.8.8
-port | 0   | Google dns          | 8.8.8.8:53
+http  | 200 | Google website        | https://google.com
+http4 | 200 | Google website (IPv4) | https://google.com
+http6 | 200 | Google website (IPv6) | https://google.com
+http  | 404 | Google 404            | https://google.com/dummy
+ping  | 0   | Google ping           | 8.8.8.8
+port  | 0   | Google dns            | 8.8.8.8 53
diff --git a/tinystatus b/tinystatus
index dbd0fad..838370b 100755
--- a/tinystatus
+++ b/tinystatus
@@ -24,17 +24,19 @@ check(){
     name="${3}"
     expectedcode="${4}"
 
-    if [ ${ctype} = 'http' ]; then
-        statuscode="$(curl -sSkLo /dev/null -H "${useragent}" -m "${timeout}" -w "%{http_code}" "${host}" 2> "${tmp}/ko/${name}.error")"
-    elif [ ${ctype} = 'port' ]; then
-        error="$(nc -w "${timeout}" -zv $(echo "${host}" | sed 's,:, ,') 2>&1)"
-        statuscode=$?
-        [ ${statuscode} -ne 0 ] && echo "${error}" > "${tmp}/ko/${name}.error"
-    elif [ ${ctype} = 'ping' ]; then
-        ping -W "${timeout}" -c 1 "${host}" >/dev/null 2>&1
-        statuscode=$?
-        [ ${statuscode} -ne 0 ] && echo 'Host unreachable' > "${tmp}/ko/${name}.error"
-    fi
+    IPv="$(echo "${ctype}" | grep -o '[0-9]$')"
+    case "${ctype}" in
+        http*)
+            statuscode="$(curl -${IPv}sSkLo /dev/null -H "${useragent}" -m "${timeout}" -w "%{http_code}" "${host}" 2> "${tmp}/ko/${name}.error")";;
+        ping*)
+            ping -W${IPv} "${timeout}" -c 1 "${host}" >/dev/null 2>&1
+            statuscode=$?
+            [ ${statuscode} -ne ${expectedcode} ] && echo 'Host unreachable' > "${tmp}/ko/${name}.error";;
+        port*)
+            error="$(nc -w${IPv} "${timeout}" -zv ${host} 2>&1)"
+            statuscode=$?
+            [ ${statuscode} -ne ${expectedcode} ] && echo "${error}" > "${tmp}/ko/${name}.error";;
+    esac
 
     # verity status and write files
     if [ ${statuscode} -eq ${expectedcode} ]; then
@@ -59,7 +61,7 @@ while IFS='\n' read -r line; do
     name="$(get_element 3 "${line}")"
     host="$(get_element 4 "${line}")"
     check "${ctype}" "${host}" "${name}" "${code}" &
-done < "${1:-checks.list}"
+done < "${checkfile}"
 wait
 
 cat << EOF