Free Online Port Checker — Test If a Port Is Open or Closed
Check if a TCP port is open, closed, or filtered on any server or IP address. Our free port checker tool tests connectivity to any host and port — perfect for verifying firewall rules, diagnosing connection issues, and ensuring your services are accessible from the internet.
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TCP Port Connectivity Test
Enter a host and port number to check if the TCP port is open and accepting connections.
Test ports 1-65535 on any host
Verify firewall rules are working
Connection test in seconds
Verify services are running and accessible
What Is a Port Checker and How Does It Work?
A port checker tests whether a specific TCP port on a remote host is open (accepting connections), closed (actively refusing connections), or filtered (blocked by a firewall with no response). When you run a port check, the tool attempts to establish a TCP connection to the specified host and port. If the three-way TCP handshake (SYN, SYN-ACK, ACK) completes successfully, the port is reported as open. If the connection is refused, the port is closed. If no response is received within the timeout period, the port is likely filtered by a firewall.
Common Ports You Should Know
Port 80 (HTTP) and Port 443 (HTTPS) are used by web servers — if your website is down, check these first. Port 22 (SSH) is used for secure remote server access. Port 21 (FTP) handles file transfers. Port 25 (SMTP), Port 587 (SMTP submission), and Port 993 (IMAP SSL) are used for email. Port 3306 (MySQL) and Port 5432 (PostgreSQL) are database ports. Port 3389 (RDP) is for Windows Remote Desktop.
When to Use a Port Checker
Use a port checker when: a website or application isn't loading (check if ports 80/443 are open), you've set up port forwarding on your router and need to verify it works, you've configured firewall rules and want to confirm ports are properly opened or blocked, you're troubleshooting why an application can't connect to a remote service, or you need to verify that a server is running and accessible from the internet.
Understanding Port Check Results
Open: The port is accepting connections — a service is running and accessible. Closed: The host is reachable but no service is listening on that port, or the OS is actively refusing connections. Filtered: A firewall, router, or ISP is blocking the connection — no response was received. Note that our port checker tests connectivity from our server's network, so results may differ from your local network due to different firewall rules or ISP restrictions.
For IP geolocation and network details, use our IP address lookup. To check DNS records for your server, try DNS lookup. For latency testing, use our ping test or traceroute. To see your public IP, use What is my IP; for VPN detection, see our VPN check tool.
Privacy, Accuracy & Security
Privacy: We don’t log your checks. Accuracy: Results show connectivity from our server; your local network may differ. Security: HTTPS only. Check only hosts you’re authorized to test.
Frequently Asked Questions About Port Checking
How do I check if a port is open on my server?
Enter your server's IP address or domain name and the port number in the tool above, then click "Check Port." The tool will attempt a TCP connection and tell you if the port is open, closed, or filtered.
Why does a port show as filtered?
A filtered port means a firewall is blocking the connection. This could be your server's firewall (iptables, Windows Firewall), your hosting provider's network firewall, or your ISP blocking certain ports. Check your firewall rules and hosting provider settings.
Is port scanning legal?
Checking ports on your own servers and systems is perfectly legal and a normal administrative task. However, scanning ports on systems you don't own without permission may violate computer crime laws in many jurisdictions. Always ensure you have authorization before scanning.
What's the difference between TCP and UDP ports?
TCP ports use connection-oriented communication with guaranteed delivery (web servers, email, SSH). UDP ports use connectionless communication with no delivery guarantee (DNS, gaming, streaming). This tool checks TCP ports. UDP port checking is more complex because UDP doesn't establish connections the same way.
Is this port checker free?
Yes, our port checker is completely free to use. No signup or API key required.