About the Open Port Checker
This tool runs a TCP connect scan from our server against 20 common ports and reports each one as open, closed or filtered: FTP (21), SSH (22), Telnet (23), SMTP (25), DNS (53), HTTP (80), POP3 (110), IMAP (143), HTTPS (443), SMTPS (465), SMTP submission (587), IMAPS (993), POP3S (995), MS SQL (1433), MySQL (3306), RDP (3389), PostgreSQL (5432), Redis (6379), HTTP alt (8080) and HTTPS alt (8443).
It answers "can the internet reach this service?", for example after opening a firewall rule or to confirm a database port is not exposed. Host names are resolved first (IPv4 preferred), all ports are tried in parallel with a 2-second timeout each, and loopback and private addresses are refused. Only scan hosts you own or are allowed to test.
How to use it
- Enter a host name or public IP address, for example
example.com. - Select Scan.
- Filter the table by state to see only open, closed or filtered ports.
Examples
- Scan example.com: typically only web ports are open.
- Scan scanme.nmap.org: a host the Nmap project provides for test scans.
- Scan dns.google: a public DNS service with port 53 open.
Common questions
What is the difference between closed and filtered?
Closed means the host answered and refused the connection (a TCP reset), so nothing is listening. Filtered means there was no reply before the timeout, usually because a firewall drops the packets.
Why is a port open for me but closed here?
You may be testing from inside the same network, a VPN or an allow-listed IP. This scan comes from the public internet, like any outside visitor.
Can this check UDP ports?
No. It only makes TCP connections, so UDP services such as DNS over UDP, QUIC or WireGuard aren't tested.
Related tools
- SSL Certificate Checker: inspect the certificate on an open TLS port such as 443 or 993.
- DNS Lookup: see the addresses the host name resolves to.
- HTTP Request Builder: send a request to an open web port.