Port Checker

The port checker tool tests whether a specific TCP port is open on any IP address or hostname. Use it to verify firewall rules, confirm that services are running and accessible, or diagnose connectivity issues. Simply enter a host and port number to get an instant result.

What Are Network Ports?

A network port is a numbered endpoint for communication in the TCP/IP protocol suite. Ports allow a single IP address to host multiple services simultaneously. Defined by a 16-bit unsigned integer, port numbers range from 0 to 65,535. When you connect to a website, your browser contacts the server’s IP address on a specific port (typically 443 for HTTPS). The combination of IP address and port number forms a socket, as described in RFC 793 (TCP) and RFC 768 (UDP).

Well-Known Ports

The most commonly used ports are reserved for standard services:

These assignments are maintained by IANA’s Service Name and Transport Protocol Port Number Registry.

How Port Checking Works

This tool performs a TCP connection attempt (sometimes called a TCP connect scan) to the specified host and port. It initiates the TCP three-way handshake: your request sends a SYN packet, and if the target responds with SYN-ACK, the port is considered open. If the connection is refused or times out, the port is reported as closed or filtered. The check is performed from our server, so the result reflects external accessibility — what the internet sees.

Open vs. Closed vs. Filtered Ports

Port scan results fall into three categories:

• Open — a service is actively listening and accepting connections on this port. The TCP handshake completed successfully.
• Closed — the host is reachable but no service is listening on this port. The server responds with a RST (reset) packet.
• Filtered — a firewall or security device is silently dropping packets. No response is received within the timeout period, making it impossible to determine if a service is running.

A filtered port is the most secure configuration for unused services, as it reveals nothing to potential attackers.

Port Number Ranges

The 65,536 available ports are divided into three ranges by RFC 6335:

• Well-Known Ports (0-1023) — reserved for system services and common protocols. Binding to these ports typically requires root or administrator privileges.
• Registered Ports (1024-49151) — assigned by IANA to specific applications upon request. Examples include 3306 (MySQL) and 5432 (PostgreSQL).
• Dynamic/Ephemeral Ports (49152-65535) — used temporarily by client applications for outbound connections. The operating system assigns these automatically.

Why Check Ports?

Port checking serves several practical purposes:

• Firewall verification — confirm that your firewall rules are correctly allowing or blocking traffic on specific ports
• Service troubleshooting — verify that a web server, database, or mail server is actually listening and reachable from the outside
• Security auditing — identify unintentionally exposed services that could present attack surfaces
• Migration testing — after moving a service to a new server, confirm it is accessible on the expected port
• ISP restrictions — determine if your internet provider is blocking certain ports like 25 (SMTP) or 80 (HTTP)

Security Considerations

Every open port is a potential entry point. Follow the principle of least exposure: only open ports that are required for your services. Use firewalls to restrict access by source IP where possible, and keep services updated to patch known vulnerabilities. Tools like this port checker help you verify your security posture by showing exactly what is visible from the public internet.

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• HTTP Header Checker — view the HTTP response headers returned by any URL