Simple Port Tester — Test Open Ports in Seconds

Simple Port Tester: Quick Network Port Check Tool

What it is
A lightweight utility that quickly checks whether a specific TCP or UDP port on a remote host is open, closed, or filtered. Designed for speed and simplicity, it’s useful for troubleshooting connectivity, firewall rules, and service availability.

Key features

• Port check (TCP & optionally UDP): Test single or multiple port numbers against an IP or hostname.
• Fast connection attempts: Short timeouts and parallel checks for quick results.
• Plain results: Reports “open”, “closed”, or “filtered/unreachable”.
• Custom timeout & retry: Adjust timeouts or retry counts to suit slow networks.
• Simple UI or CLI: Minimal graphical interface or command-line usage for scripting.
• Logging/export: Save results to a log file or CSV for audits.
• Lightweight: Low resource usage; works on Windows, macOS, and Linux.

Common uses

• Verify whether a server is accepting connections on a given port (e.g., SSH 22, HTTP 80, HTTPS 443).
• Troubleshoot firewall or NAT issues by checking externally visible ports.
• Confirm that a port-forwarding rule is functioning.
• Quick pre-deployment checks to ensure required services are reachable.

How it works (brief)

• For TCP, the tester attempts a TCP handshake to the target port; success = open, immediate refusal = closed, no response within timeout = filtered/unreachable.
• For UDP (if supported), it sends a datagram and interprets ICMP unreachable responses or lack of response per configured timeout.

Example CLI usage

• Check a single port: porttester –host example.com –port 22
• Check multiple ports in parallel: porttester –host 198.51.100.5 –ports 22,80,443 –timeout 2s –parallel 10
• Save results: porttester –host myserver.local –ports 80,443 –output results.csv

Limitations & cautions

• UDP checks are less reliable due to protocol nature and intermediate devices dropping packets silently.
• Scanning many hosts/ports may trigger intrusion detection systems or violate acceptable-use policies — use with permission.
• Results show reachability from the tester’s network only; remote network conditions may differ.

Alternatives

• Built-in tools: telnet, nc (netcat), nmap (richer scans).
• Online port checkers (for testing external visibility).