How to use the port checker
- Enter the hostname or public IP address of the server you manage.
- Pick the port from the list of common services (SSH, HTTPS, SMTP, databases and so on) and press Check port.
- Read the verdict: open means something is listening, closed means the host refused, filtered means nothing answered before the timeout, which usually points at a firewall.
- Switch to TCP ping to run four connects to port 443 or 80 and see the minimum, average and maximum handshake time.
Features
- Open, closed, filtered or unreachable, each explained in plain words
- Handshake time in milliseconds, a practical TCP ping that works even when ICMP ping is blocked
- Nineteen common service ports, chosen from a list rather than typed, so no ranges and no guessing
- TCP ping mode with min, average, max and loss across four sequential connects
- Private, loopback, link-local and other non-public targets refused before any connection is made
What the three answers mean
Open: the TCP three-way handshake completed, so a service is accepting connections on that port. It says nothing about whether the service works, only that it answers.
Closed: the host replied with a reset. It is up and reachable, but nothing is listening on that port. This is the answer you get when a service has stopped or is bound to a different port.
Filtered: no reply arrived within four seconds. Packets are being dropped somewhere along the path, almost always by a firewall or security group. A host that is entirely offline also looks filtered, so check with the TCP ping on port 443 or 80 first.
Authorised use only
This is a diagnostic for servers you own or are responsible for: confirming a firewall rule, checking that a mail or database port is reachable from outside, or proving to a hosting provider that a port is blocked. It deliberately tests one host and one port per request, offers only common service ports, reads no banners and never scans ranges. Please do not point it at systems you do not administer.
Requests are limited to ten per minute per visitor, and every target is validated against a public-address allow-list before any socket is opened.
Why the result can differ from what you see
The connection starts from VoltKit's hosting region. Firewalls that allow only certain countries or networks, providers that block outbound ports, and services that rate-limit unknown clients can all produce a different answer for you. Treat a filtered result as 'unreachable from here', not as a universal fact.