diff --git a/notify/slack.sh b/notify/slack.sh
new file mode 100644
index 0000000..cc1ed76
--- /dev/null
+++ b/notify/slack.sh
@@ -0,0 +1,55 @@
+#!/usr/bin/env sh
+
+#Support Slack webhooks
+
+#SLACK_WEBHOOK_URL=""
+#SLACK_CHANNEL=""
+#SLACK_USERNAME=""
+
+slack_send() {
+  _subject="$1"
+  _content="$2"
+  _statusCode="$3" #0: success, 1: error 2($RENEW_SKIP): skipped
+  _debug "_statusCode" "$_statusCode"
+
+  SLACK_WEBHOOK_URL="${SLACK_WEBHOOK_URL:-$(_readaccountconf_mutable SLACK_WEBHOOK_URL)}"
+  if [ -z "$SLACK_WEBHOOK_URL" ]; then
+    SLACK_WEBHOOK_URL=""
+    _err "You didn't specify a Slack webhook url SLACK_WEBHOOK_URL yet."
+    return 1
+  fi
+  _saveaccountconf_mutable SLACK_WEBHOOK_URL "$SLACK_WEBHOOK_URL"
+
+  SLACK_CHANNEL="${SLACK_CHANNEL:-$(_readaccountconf_mutable SLACK_CHANNEL)}"
+  if [ -n "$SLACK_CHANNEL" ]; then
+    _saveaccountconf_mutable SLACK_CHANNEL "$SLACK_CHANNEL"
+  fi
+
+  SLACK_USERNAME="${SLACK_USERNAME:-$(_readaccountconf_mutable SLACK_USERNAME)}"
+  if [ -n "$SLACK_USERNAME" ]; then
+    _saveaccountconf_mutable SLACK_USERNAME "$SLACK_USERNAME"
+  fi
+
+  export _H1="Content-Type: application/json"
+
+  _content="$(printf "*%s*\n%s" "$_subject" "$_content" | _json_encode)"
+  _data="{\"text\": \"$_content\", "
+  if [ -n "$SLACK_CHANNEL" ]; then
+    _data="$_data\"channel\": \"$SLACK_CHANNEL\", "
+  fi
+  if [ -n "$SLACK_USERNAME" ]; then
+    _data="$_data\"username\": \"$SLACK_USERNAME\", "
+  fi
+  _data="$_data\"mrkdwn\": \"true\"}"
+
+  if _post "$_data" "$SLACK_WEBHOOK_URL"; then
+    # shellcheck disable=SC2154
+    if [ "$response" = "ok" ]; then
+      _info "slack send success."
+      return 0
+    fi
+  fi
+  _err "slack send error."
+  _err "$response"
+  return 1
+}