Port Checker
Check if a TCP port is open or closed on any host.
What Is a Port Checker?
A port checker tests whether a specific TCP port on a remote host is open and accepting connections. Common ports: 22 (SSH), 80 (HTTP), 443 (HTTPS), 3306 (MySQL), 5432 (PostgreSQL).
Open vs Closed
Common Use Cases
- Firewall verification — confirm a port you just opened is actually reachable from outside your network.
- Security audits — check for unintentionally exposed services like databases or admin panels running on non-standard ports.
- Service deployment checks — verify a newly deployed application (e.g. on port 3000, 8080) is accessible before going live.
- VPN/proxy configuration — confirm required ports for VPN protocols (e.g. 1194 for OpenVPN) are open and not blocked by an ISP or firewall.
Example
Checking port 5432 (PostgreSQL's default) and finding it open to the public internet is a common and serious misconfiguration — database ports should typically be firewalled to specific IPs only.
Frequently Asked Questions
What does 'filtered' mean versus 'closed'?
Closed means the port actively refused the connection. Filtered means no response was received at all, usually because a firewall is silently dropping the traffic.
Is it safe to leave any ports open?
Only ports required for services you intend to expose publicly (e.g. 80/443 for a web server) should be open. Everything else should be firewalled by default.
Why is my port closed even though the service is running?
This usually means a firewall (on the server itself, a cloud provider's security group, or your router) is blocking external access to that port.
What ports are commonly targeted by attackers?
22 (SSH), 3389 (RDP), 3306/5432 (databases), and 23 (Telnet) are frequently scanned and targeted if left exposed without proper authentication.