1. Enter the public host
Use a hostname such as example.com or a public IP address. If you use a hostname, remember that DNS decides which address is tested.
IP Protocol Tools
Open Port Checker Online
Use this open port checker tool to test one public TCP service on a website, server, router, hostname, IPv4 address, or public IPv6 address and understand what the result means.
Single port checkOne host and one TCP port per request; no ranges or lists.
Not a scannerDesigned for service validation, not discovery or bulk probing.
Fast timeoutShort connection attempts keep results practical and bounded.
Working tool
Online open port checker tool
Enter one public hostname or IP address and one TCP port. The tool attempts a TCP connection from the Netest server; it does not scan ranges or private networks.
Ready. Example input: example.com on TCP 443
What does an open port check prove?
An open result means the Netest server completed a TCP handshake with the selected host and port. It confirms basic network reachability to a listening service, but it does not prove that the application is healthy, correctly configured, or safe. A closed result means the host refused the connection. A timeout means no clear reply arrived and may indicate filtering, routing trouble, or a service that is not publicly exposed.
How to check a TCP port
2. Enter one TCP port
Use a number from 1 to 65535, such as 443 for HTTPS, 22 for SSH, or 25 for SMTP. Check only services you own or are authorized to test.
3. Confirm at the application layer
If the port is open, continue with a protocol-specific test. For HTTPS, check the certificate, headers, status code, and backend health.
How the port checker works
The server resolves the hostname when necessary, rejects non-public destinations, and attempts a short TCP connection to the selected port. The result reflects the path from Netest to the destination at that moment.
Single port only
The tool accepts one TCP port number and rejects ranges, lists, and bulk checks.
Public hosts only
Private and reserved IP ranges are blocked so the tool cannot be used against internal networks.
External viewpoint
A service may be reachable from Netest but blocked from your office, or reachable internally but blocked from the public Internet. Compare both viewpoints.
Port check examples
| Input | Typical output | Meaning |
|---|---|---|
| example.com, 443 | open, TCP connection completed | The HTTPS port accepted a TCP connection. |
| example.com, 25 | closed, filtered, or timeout | The service may be unavailable, blocked, or not listening from this path. |
How to interpret a port check
A port check answers one narrow question: can the Netest server complete a TCP connection to this host and port? It does not log in, send an application request, or prove the full service is healthy. For example, TCP 443 can be open while the website still fails because of a bad certificate, wrong virtual host, failed backend pool, or application error.
Open
The TCP handshake completed. Continue with protocol-specific checks such as SSL Checker, HTTP Header Checker, or application logs.
Closed
The host responded but no service accepted the connection on that port. Check listener configuration, firewall rules, and load balancer mappings.
Timeout or filtered
No clear response came back. This often points to filtering, upstream security policy, routing issues, or a service exposed only to trusted networks.
Common port-checking problems
Port range entered
Inputs such as 20-25 or 80,443 are rejected. Use one port at a time.
Filtered timeout
A firewall may silently drop the connection attempt, making the result look like a timeout.
Closed port
A refused connection usually means the host answered but no service is listening on that TCP port.
When to use this port checker
- Verify that a newly published HTTPS, SSH, SMTP, database proxy, or VPN service is reachable from the Internet.
- Check a firewall, NAT, security-group, or load-balancer rule after an approved change.
- Confirm whether the service listener is exposed before troubleshooting the application itself.
- Compare a hostname test with a direct public-IP test to separate DNS from TCP reachability.
- Recheck during an incident to see whether the result changes after a rollback or failover.
Check an open port on a server, router, Windows, or Mac
Server or website open port checker
Enter the server's public IP address or hostname and the single TCP service port. For a website, test 443 for HTTPS or 80 for HTTP, then use an application-level checker if the TCP port opens.
Router open port checker
Enter the router's public WAN address or public hostname and the forwarded TCP port. The NAT or port-forwarding rule, firewall policy, and internal service listener must all be correct for the result to be open.
Open port checker command on Windows
In PowerShell on Windows 10 or later, run Test-NetConnection example.com -Port 443. To inspect local listeners, use netstat -ano. Only test systems you own or are authorized to administer.
Open port checker command on Mac
On macOS, run nc -vz example.com 443 to test a remote TCP port. Use lsof -nP -iTCP -sTCP:LISTEN to inspect local TCP listeners.
IP and IPv6 open port checker
The tool accepts a public IPv4 or IPv6 address. IPv6 results depend on routing and firewall connectivity between the Netest server and the destination; private, loopback, local, multicast, and reserved targets are blocked.
Open Port Checker: FAQ
Is this a port scanner?
No. It checks exactly one TCP port per request and does not support ranges, lists, or bulk targets.
Does open mean the application works?
No. Open only means the TCP handshake completed. The application protocol may still fail authentication or health checks.
Is this a UDP open port checker?
No. This page checks TCP only. UDP has no TCP-style handshake and normally requires a protocol-specific request and response to determine whether a service is reachable.
Can this tool check all open ports?
No. An “all open port checker” is a port scanner. This safety-focused tool checks one explicitly selected TCP port and rejects ranges, lists, and service scans.
Can I run a local open port check?
Not with this online checker. Private and local targets are blocked. Use netstat, ss, or lsof on an authorized device to inspect its listening ports.
Do I need an open port checker download?
No. This tool runs online in a browser. A local command-line tool is useful only when you need the result from your own computer or network viewpoint.
How does this compare with YouGetSignal's open port checker?
Both are intended to test whether a selected public service is reachable. This Netest tool checks one TCP port, explains open, closed, and timeout states, and blocks private targets and port ranges. Networking Essentials is not affiliated with or endorsed by YouGetSignal.