Free Open Port Checker
Test if any TCP/UDP port is open or closed on any server or IP address — instant results, no signup needed
How to Check Open Ports — Port Checker Guide
Web Services
80- HTTP443- HTTPS8080- HTTP Alternative8443- HTTPS Alternative
Mail Services
25- SMTP587- SMTP (TLS)143- IMAP993- IMAP (SSL)110- POP3995- POP3 (SSL)
Database Services
3306- MySQL5432- PostgreSQL27017- MongoDB6379- Redis
Remote Access
22- SSH3389- RDP21- FTP23- Telnet
Frequently Asked Questions
What does it mean if a port is open?
An open port means a service is listening on that port and accepting TCP connections from the network. This is expected for public-facing services like web servers (port 80/443) or mail servers (port 25).
What does it mean if a port is closed?
A closed port means either no service is running on that port, or a firewall is blocking access from the internet. A closed port on a database server (e.g., 3306) is usually intentional and correct for security.
Why can't I check some ports?
Some ports may be blocked by your ISP or a network firewall before they reach the target server. Ports like 25 (SMTP) are often blocked by ISPs to prevent spam relaying.
Is it safe to have ports open?
Open ports are necessary for services to work, but each open port increases your attack surface. Only expose ports that must be publicly accessible, use firewalls to restrict the rest, and keep services patched.
What are the most common ports to check?
The most commonly tested ports are: 80 (HTTP), 443 (HTTPS), 22 (SSH), 21 (FTP), 25 (SMTP), 3306 (MySQL), 5432 (PostgreSQL), 6379 (Redis), 3389 (RDP), and 8080 (HTTP alternative).
What is the difference between TCP and UDP ports?
TCP (Transmission Control Protocol) ports use a three-way handshake, making them reliably testable. UDP (User Datagram Protocol) ports are connectionless and much harder to probe remotely — most online port checkers test TCP only.
How do I check if a firewall is blocking a port?
Run this port checker from outside your network. If the port shows as closed but you expect it to be open, your firewall (server firewall, cloud security group, or network firewall) may be blocking it. Check your iptables, ufw, or cloud provider security group rules.
How can I monitor port availability continuously?
For one-time checks this tool is ideal. For ongoing port monitoring with instant alerts when a port goes down, AlertSleep monitors TCP/UDP ports every minute and notifies you via email, Slack, or SMS.
Want Automated Monitoring?
Get 24/7 monitoring with instant alerts when issues are detected.
Start Free Trial