Free Online Port Checker

What is a port checker?

A port checker tests whether a specific TCP port on a remote host is accepting connections. When a port is "open", it means there is a service listening on that port and it is reachable from your current network. When a port is "closed" or "filtered", either no service is running on that port or a firewall is blocking the connection.

Common ports and their services

Why would a port appear closed?

A port can appear closed for several reasons: no service is listening on that port, a firewall (like AWS Security Groups, UFW, or iptables) is blocking the connection, or the host is offline. If you expect a port to be open, use our IP Whitelist Config Generator to add your IP to the relevant firewall rules.

• IP Whitelist Config Generator — Detect your IP and generate AWS, MongoDB, GCP configs
• Port Checker — Test if TCP ports are open on any host
• DNS Lookup — Query A, AAAA, MX, CNAME, TXT and NS records
• WHOIS Lookup — Find domain owner, registrar, and expiry date
• SSL Checker — Verify SSL certificate validity and expiry
• IP Location Map — Find any IP location on an interactive map
• HTTP Headers Checker — Inspect request and security headers
• Latency Test — Measure your RTT to major cloud regions
• User Agent Parser — Full browser and OS fingerprint breakdown
• IPv6 Detector — Check your IPv6 address and connectivity

How to check if a port is open from the command line

Without a port checker tool, you can test port connectivity directly from your terminal. On Linux and macOS, use nc -zv hostname port (netcat) or telnet hostname port. On Windows, use Test-NetConnection -ComputerName hostname -Port port in PowerShell.

For example, to check if port 443 is open on a server: nc -zv example.com 443. If the connection succeeds, the port is open. If it times out or refuses, the port is closed or blocked by a firewall.

What is the difference between TCP and UDP ports?

TCP ports (Transmission Control Protocol) require a three-way handshake before data is exchanged, making them reliable and ordered. Web servers (port 80, 443), SSH (port 22), and databases (MySQL port 3306, PostgreSQL port 5432, MongoDB port 27017) all use TCP.

UDP ports (User Datagram Protocol) send data without establishing a connection first. This makes UDP faster but less reliable. DNS (port 53), NTP (port 123), and gaming protocols commonly use UDP. This port checker tests TCP ports only, as UDP port testing requires a different approach.