Apex domains cannot have CNAME records.
Question and response
Question
dig sensi.tools. NS
Answer
sensi.tools. 5 NS ns1019.ui-dns.org.
sensi.tools. 5 NS ns1069.ui-dns.com.
sensi.tools. 5 NS ns1053.ui-dns.biz.
sensi.tools. 5 NS ns1095.ui-dns.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0