Port Checker (TCP & UDP)
Enter a host for the usual ports, host:port for one port, or a list like host:80,443,53. TCP and UDP are checked together.
- via Check-Host.net
TCP and UDP together
Every port is tested over TCP and UDP in a single run. A host without a port gets the common ports (web, mail, SSH, databases, DNS, NTP, STUN, QUIC). For one TCP port you also see how it answers from servers around the world.
Open, closed or filtered
Open means something answered. Closed means the host refused the connection. Filtered means nothing came back, usually a firewall. UDP is quiet by design, so “no reply” can mean open-but-silent or filtered; only services that answer a probe show as open.
Typical uses
Check that a server you have just set up is reachable from the internet, that a firewall rule really opens or closes a port, that a game, VoIP or VPN server answers over UDP, or that a mail server listens on 25, 465 and 587. For a single TCP port you also see whether it can be reached from other countries.
Frequently asked questions
What is the difference between closed and filtered?
Closed: the host actively refused. Filtered: no answer at all, typically a firewall dropping packets.
Why does UDP often say “no reply”?
UDP has no handshake. A port can be open and still say nothing unless it receives a request it understands. We send DNS, NTP, STUN or QUIC probes where they fit.
Can I check several ports?
Yes. Write them after the host, separated by commas: example.com:80,443,53 (up to 20 ports).
Why is a port open here but closed somewhere else?
Firewalls and geo-blocking can allow only some networks. The worldwide comparison shows which locations can reach the port.