Port Checker
What Is a Port Checker?
A port checker tests whether a specific TCP port on a host is open and accepting connections. In computer networking, ports are numbered endpoints (0-65535) that identify specific services running on a server. When data arrives at a server's IP address, the port number determines which application should handle the request. Our tool attempts to establish a TCP connection to the specified host and port, reporting whether the port is open or closed.
Understanding which ports are open on your servers is essential for both functionality and security. Web servers need port 80 (HTTP) and 443 (HTTPS) open to serve content. Email servers require port 25 (SMTP) for receiving mail and port 587 for submission. SSH access uses port 22, while database services like MySQL (3306) and PostgreSQL (5432) also listen on specific ports. If an expected port is closed, the associated service is unreachable.
From a security perspective, every open port represents a potential entry point. Attackers scan for open ports to identify running services and look for vulnerabilities. Best practice is to follow the principle of least privilege: only open the ports that are strictly necessary for your services, close everything else with a firewall, and regularly audit which ports are exposed. Services that do not need to be publicly accessible should be restricted to specific IP addresses or VPN connections.
Common TCP ports you should know include: 21 (FTP file transfer), 22 (SSH secure shell), 25 (SMTP email delivery), 53 (DNS queries), 80 (HTTP web traffic), 110 (POP3 email retrieval), 143 (IMAP email access), 443 (HTTPS encrypted web traffic), 465 (SMTPS encrypted email), 587 (SMTP submission), 993 (IMAPS encrypted IMAP), 995 (POP3S encrypted POP3), 3306 (MySQL database), 3389 (Windows Remote Desktop), 5432 (PostgreSQL database), and 8080 (HTTP alternate, often used for development or proxies).
After checking ports, use our Ping Test to measure connectivity and latency, analyze HTTP security headers for web-facing services, or test SMTP connectivity for mail servers.
Frequently Asked Questions
What is a port in networking?
A port is a numbered endpoint on a computer that identifies a specific process or service. Ports range from 0 to 65535. The port number tells the operating system which application should handle incoming data.
What are the most common TCP ports?
Common TCP ports include: 21 (FTP), 22 (SSH), 25 (SMTP), 53 (DNS), 80 (HTTP), 110 (POP3), 143 (IMAP), 443 (HTTPS), 587 (SMTP submission), 993 (IMAPS), 3306 (MySQL), 3389 (RDP), 5432 (PostgreSQL), and 8080 (HTTP alternate).
What does open and closed mean for a port?
An open port means a service is actively listening and accepting connections. A closed port means no service is listening or a firewall is blocking the connection. A filtered port means a firewall is silently dropping packets.
Is it safe to have open ports?
Open ports are necessary for services to function, but unnecessary open ports increase the attack surface. Best practice is to open only required ports, keep software updated, use firewalls, and regularly scan for unexpected open ports.