A network port is a logical endpoint on a device for a specific type of network communication. When a server runs a web server, it listens on port 80 (HTTP) or port 443 (HTTPS). An SSH server listens on port 22. A database server listens on a port specific to the database software. Checking whether a port is open tells you whether the service on that port is reachable from the network.
What a Port Check Actually Tests
A port check attempts a TCP connection to the specified host and port number. If the connection succeeds (the server accepts the connection), the port is open and the service is reachable. If the connection is refused (the server explicitly rejects it), no service is listening on that port. If the connection times out (no response at all), a firewall is blocking the connection.
The distinction between refused and timed-out is significant. A refused connection means you reached the server but nothing is listening. A timed-out connection means a firewall is preventing the packets from arriving, or the host is not reachable.
Common Port Numbers
Port 22 is SSH (Secure Shell), used for remote server administration. Port 25 is SMTP, used for sending email between mail servers. Port 80 is HTTP, unencrypted web traffic. Port 443 is HTTPS, encrypted web traffic. Port 3306 is MySQL database connections. Port 5432 is PostgreSQL database connections. Port 6379 is Redis. Port 27017 is MongoDB.
Many applications use custom or non-standard ports. Check your service documentation for the specific port number.
Why Port Checking Matters
Deployment verification: after deploying a service, check that it is listening on the expected port before pointing DNS or load balancer configuration at it.
Firewall debugging: if a service is running but not reachable, a port check distinguishes between a service that is not listening and a firewall that is blocking access.
Security auditing: checking which ports are open on a server from an external perspective reveals what attack surface is exposed to the internet. Any port that is open but not necessary should be closed.
Using the DevHexLab Port Checker
Open the tool at /tools/developer/port-checker. Enter the hostname or IP address. Enter the port number. Click Check. The result tells you whether the port is open, closed, or filtered (timed out).
Frequently Asked Questions
Can I check ports on localhost or my home network?
No. The tool checks ports from its own server on the public internet. To check localhost or a private network address, use a local tool like telnet or the nc (netcat) command.
Is checking open ports on a server I do not own legal?
Port scanning servers you do not own can be considered a hostile act and may violate terms of service or laws depending on your jurisdiction. Only check ports on servers you own or have explicit permission to test.
A port check is the quickest way to verify that a service is reachable before diving into application logs.