What is a port checker?
A port checker tests whether a TCP connection can be established to a specific port on a public hostname or IP address. It can help verify whether a web server, remote-access service, database gateway or another Internet-facing TCP service is reachable.
For example, checking TCP port 443 can help determine whether an HTTPS endpoint accepts TCP connections, while port 3389 is commonly associated with Microsoft Remote Desktop.
What does an open port mean?
An open TCP port means that a TCP connection could be established to the specified host and port from the network location performing the test.
It does not necessarily identify which application is running on the port, and it does not confirm that the application itself is healthy beyond accepting the TCP connection.
What does closed or unreachable mean?
A failed connection may mean that no service is listening on the selected port. It can also mean that a firewall, router, security group or network policy is blocking the connection.
Some firewalls silently drop unwanted connections rather than actively rejecting them. In that situation, the result may appear as a timeout rather than a definite closed-port response.
Common ports to check
| Port | Service | Typical Use |
|---|---|---|
| 22 | SSH | Secure remote access |
| 53 | DNS | DNS service over TCP |
| 80 | HTTP | Web traffic |
| 443 | HTTPS | Encrypted web traffic |
| 445 | SMB | File and printer sharing |
| 587 | SMTP Submission | Email submission |
| 993 | IMAPS | Secure IMAP email access |
| 1433 | SQL Server | Microsoft SQL Server |
| 3306 | MySQL | MySQL database |
| 3389 | RDP | Remote Desktop |
| 5432 | PostgreSQL | PostgreSQL database |
| 8080 | HTTP Alternate | Alternate web services |
How to use the port checker
- Enter the public hostname or public IP address of a system you are authorized to test.
- Enter one TCP port number from 1 through 65535.
- Click Check Port.
- Review whether the TCP connection was reachable, timed out or could not be established.
Port checker vs port lookup
A port checker performs a network connectivity test against a specific host and TCP port. A port lookup is different: it tells you which service is commonly associated with a port number without connecting to the destination.
Why can a port appear closed?
The application may not be running, the service may be bound only to a private interface, a firewall may block inbound traffic, NAT or port-forwarding may be missing, or a cloud security rule may prevent access.
Frequently asked questions
How can I check whether port 443 is open?
Enter the public hostname or IP address, set the port to 443 and run the check. A successful TCP connection means the port is reachable from the checker's network.
What does a port timeout mean?
A timeout means no successful connection was established within the allowed period. A firewall may be silently dropping traffic, or the destination may be unreachable.
Can an open port still have a broken application?
Yes. This checker confirms basic TCP connectivity only. The application behind the port can still be misconfigured or unhealthy.
Does this test UDP ports?
No. This tool currently checks TCP connectivity only. UDP does not use the same connection-establishment process as TCP.
Can I check private IP addresses?
No. This public tool is limited to public Internet destinations and does not test private, loopback or local-network addresses.
Why might I get a different result from another location?
Firewall policies, routing, geographic filtering and source-IP restrictions can cause a service to be reachable from one network location but not another.