Apex domains cannot have CNAME records.
Question and response
Question
dig nic.tools. NS
Answer
nic.tools. 5 NS v0n3.nic.tools.
nic.tools. 5 NS v0n1.nic.tools.
nic.tools. 5 NS v0n0.nic.tools.
nic.tools. 5 NS v0n2.nic.tools.
nic.tools. 5 NS v2n1.nic.tools.
nic.tools. 5 NS v2n0.nic.tools.
Authority
The response has no authority records.
Additional
v0n0.nic.tools. 171021 A 65.22.28.44
v0n2.nic.tools. 171021 A 65.22.30.44
v2n1.nic.tools. 171021 A 161.232.15.44
v0n0.nic.tools. 171021 AAAA 2a01:8840:1e:0:0:0:0:44
v0n2.nic.tools. 171021 AAAA 2a01:8840:20:0:0:0:0:44
v2n1.nic.tools. 171021 AAAA 2a01:8840:f9:0:0:0:0:44
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0