Port Checker
Understand how to test if a TCP port is open, find your public IP, and use a common-ports reference. Explains why real port checks need a server.
About the Port Checker
This page helps you check whether a TCP port is reachable — and is honest about how that check works. Opening a raw TCP connection to an arbitrary host and port is something browser JavaScript deliberately cannot do: the fetch, XHR and WebSocket APIs are governed by cross-origin rules and never expose TCP-level results, so a trustworthy port check needs a server-side probe.
Rather than show unreliable results, the tool explains what a real port check does — attempt a TCP connection with a short timeout and report open, closed (refused) or timed out (firewalled) — and gives you the pieces you can use right now. It fetches your public IP from a CORS-friendly API so you can test your own network, and points you to trusted external checkers and the exact terminal commands to run yourself.
A reference table of the most common ports (SSH, HTTP, HTTPS, database and mail ports and more) rounds it out, so you know what should be listening where. Your IP lookup is the only network request; nothing else leaves the page.
How to Use the Port Checker
- 1Read why a genuine TCP port check can't run entirely in the browser.
- 2Click 'Show my public IP' to get the address to test against.
- 3Use a linked external checker, or run nc -zv or Test-NetConnection from your terminal.
- 4Consult the common-ports table to know what should be listening.
Frequently Asked Questions
Why can't the browser check a port directly?
Browsers don't allow raw TCP sockets from JavaScript. The fetch, XHR and WebSocket APIs only speak specific protocols and are restricted by cross-origin security rules, and none of them report whether an arbitrary host:port completed a TCP handshake. A real port check therefore has to run from a server, which is why this tool explains the process instead of faking a result.
How can I actually test a port myself?
From your own machine you can run nc -zv host 443 on macOS or Linux, or Test-NetConnection host -Port 443 in Windows PowerShell. These attempt a real TCP connection and report success or failure. The page also links to trusted web-based checkers that probe from their own servers.
Why do I need my public IP?
To check whether a service on your own network is reachable from the internet, a checker must probe your public IP — not your private LAN address like 192.168.x.x. The tool fetches your public IP so you can paste it into an external checker.
What do open, closed and timed out mean?
Open means a service accepted the TCP connection. Closed means the host actively refused it (nothing is listening on that port). Timed out usually means a firewall silently dropped the request, so you can't tell whether anything is behind it. These three outcomes are what a server-side probe reports.