What to run
Use Port Check. The result is from Cloudflare.
How to read the result
Reachable means connect() succeeded.
A timeout or reset is not proof the port is closed. Firewalls drop packets.
The check is one port, not a sweep, and private addresses are rejected.
What to open next
For 80/443, prefer Is This Website Down and SSL Expiry Checker. Those results are from Cloudflare.
Port Check does not speak HTTP or TLS.