Port 1883 (TCP) — MQTT

MQTT message broker (plain).

🔒 Runs locally — your input never leaves this browser tab

Use MQTT over TLS (8883) with authentication.

Check if port 1883 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':1883 '

From another machine, test reachability:

nc -zv your-server.example.com 1883

With UFW (Ubuntu/Debian):

sudo ufw deny 1883

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=1883/tcp && sudo firewall-cmd --reload