Open port checker
Test whether TCP ports on a host are reachable from the public internet — checked from outside your network, which is the only view that counts.
Why check from outside?
Testing a port from the machine itself, or from the same LAN, tells you the service is running. It does not tell you whether the world can reach it. Firewall rules, cloud security groups, NAT and ISP blocks all sit between the two, and each can silently drop traffic. This tool connects from our server, so a result of "open" means genuinely reachable.
What the states mean
- Open — a TCP handshake completed. Something is listening and accepting connections.
- Closed / refused — the host answered with a reset. It is online, but nothing is listening on that port.
- Filtered / timed out — no answer at all. A firewall is dropping the packets, which is what a well-configured firewall should do.
Ports that should not be open to the world
If 3306 (MySQL), 5432 (PostgreSQL), 6379 (Redis), 27017 (MongoDB) or 3389 (RDP) answer from the public internet, fix that today. Databases belong behind a private network or a VPN; exposed Redis and Mongo instances are found and drained by automated scanners within hours. Port 22 being open is normal, but pair it with key-only authentication.
This tool checks connectivity to hosts you specify one at a time. It is for diagnosing your own servers, not for sweeping networks you do not run.
FAQ
My port is open locally but shows as filtered here
The service is bound to 127.0.0.1 rather than all interfaces, or a firewall is dropping outside traffic. Check what the service is listening on first, then the firewall.
Is having port 80 open a security problem?
No. It is how HTTP works. Redirect it to HTTPS and add HSTS, and open port 80 is simply a doorway to the secure version.
Can I check a port on a home router?
Yes, if you know the public IP. Bear in mind many ISPs block inbound 25, 80 and 445 on residential lines regardless of your own configuration.
Related reading
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