What is a port scanner?

A port scanner tests which network ports on a server are open and listening for connections. Each port corresponds to a specific service — port 80 is HTTP, 443 is HTTPS, 22 is SSH, 25 is SMTP. Open ports tell you which services are running and reachable. Port scanning is a standard step in network administration and security assessments.

How do I check which ports are open on a server?

Enter the domain name or IP address in the field above and click Scan. The tool runs an nmap-style TCP scan against the most common ports and reports which are open, closed, or filtered. Open ports are accepting connections; closed ports actively refuse them; filtered ports are blocked by a firewall and return no response.

What does it mean when a port is open?

An open port means a service is actively listening on that port and will accept incoming TCP connections. This is expected for intentionally public services (e.g. port 443 for a web server) but may indicate misconfiguration or an unintended service if found on an unexpected port. Security reviews look for open ports that should not be exposed to the internet.

Which ports should I check?

The most commonly checked ports are: 22 (SSH), 25/587/465 (SMTP/email), 80 (HTTP), 443 (HTTPS), 3306 (MySQL), 5432 (PostgreSQL), 3389 (RDP), 8080/8443 (alternative HTTP/HTTPS). The scanner covers all of these by default. For a full picture, also check 21 (FTP), 23 (Telnet — should always be closed), and 6379 (Redis).

Is port scanning legal?

Port scanning your own servers or systems you have explicit written permission to test is legal and standard practice. Scanning third-party servers without authorization is illegal in many jurisdictions and violates most hosting providers' acceptable use policies. This tool is intended for security assessments of your own infrastructure or systems you have permission to test.

What is the difference between TCP and UDP?

TCP (Transmission Control Protocol) is connection-oriented — it establishes a handshake before sending data, making it reliable and easy to scan. UDP (User Datagram Protocol) is connectionless and faster, used for DNS (port 53), NTP (123), and game servers. TCP scanning is straightforward; UDP scanning is slower and less reliable because closed UDP ports don't always respond.