Port Checker

Test whether a TCP port accepts connections on a public internet hostname or IP. Enter a host and port (1–65535) to run a single connect probe from the ToolsLibrary network API and see open, closed, or filtered status with round-trip latency. Quick-pick buttons cover common services like 22 (SSH), 25 (SMTP), 80/443 (HTTP/S), and 3306 (MySQL). Use only on systems you own or have explicit authorization to test — port scanning without permission may violate law or provider terms.

How to Use the Port Checker

Enter a public hostname or IP and a TCP port number to see whether the port accepts connections from the ToolsLibrary network probe.

  1. Open Port Checker.
  2. Enter a public Host (domain or IP) you are authorized to test.
  3. Type a Port number (1–65535) or click a common-port quick-pick chip.
  4. Click Check port and wait for the probe to complete.
  5. Read the OPEN or CLOSED / FILTERED badge and latency in milliseconds.
  6. Note the Checked timestamp — firewalls and cloud security groups may change over time.
  7. If testing a web service, follow up with Website Uptime Checker or SSL Certificate Checker for HTTP/TLS details.

How TCP connect probes work

The ToolsLibrary API attempts a single outbound TCP connection to host:port with a timeout. Success implies the port is open at the network layer from the probe origin; failure may indicate closed ports, filtering, or routing blocks.

Worked example

  • Verify SSH (22) is reachable after opening a cloud firewall rule — expect OPEN with low latency.
  • Confirm 443 is open after deploying a new load balancer before debugging certificate issues.
  • CLOSED on 3306 from the internet is often correct — databases should usually not be publicly exposed.

Common mistakes

  • Testing localhost or private IPs — the remote probe cannot reach your LAN.
  • Assuming filtered means the service is down — your ISP or host may allow only certain source networks.
  • Running repeated checks on third-party infrastructure without permission.

Limitations and acceptable use

One port per request, TCP only, single vantage point. Not a replacement for nmap, vulnerability scanning, or compliance testing. Use responsibly on infrastructure you control.

FAQ

Does this scan all ports on a host?

No. Each check tests exactly one TCP port you specify. There is no multi-port or stealth scan mode.

What is the difference between closed and filtered?

Open means a TCP connection succeeded. Closed or filtered means the probe could not connect — often due to a closed port, firewall drop, or timeout.

Where does the probe originate?

The TCP connect attempt runs from the ToolsLibrary server-side network API, not from your local computer. Results reflect reachability from that environment.

Can I check UDP ports?

No. This tool performs TCP connect probes only. UDP services require different testing methods.

Why does port 443 show open but my site does not load?

An open port only means TCP accepts connections. TLS misconfiguration, HTTP errors, or application failures can still make the service unusable in a browser.

Can I test private IP addresses?

The server can only reach publicly routable hosts. Private LAN addresses (10.x, 192.168.x) are not reachable from the internet.

Is port scanning allowed?

Test only hosts you administer or have written permission to probe. Unauthorized scanning can violate computer misuse laws and cloud provider acceptable-use policies.

Why might results differ from my local nmap?

Different source IP, geographic path, and firewall rules apply. A port open to the ToolsLibrary server may be blocked to your home IP or vice versa.

What are the quick-pick port buttons for?

They set common service ports — 22 SSH, 25 SMTP, 80 HTTP, 443 HTTPS, 3306 MySQL, and others — so you do not have to type them manually.

Does an open port mean the service is secure?

No. It only confirms TCP reachability. Security depends on authentication, patching, and firewall policy — use dedicated security tools for audits.