Open port checker
Check whether a TCP port is open on your public IP address or any server. Useful for port forwarding, game servers, Plex, CCTV and remote access.
How the open port checker works
When you press Check, our server, out on the public internet, tries to open a TCP connection to the address and port you chose, exactly as a game client or remote viewer would. If the other side completes the handshake, the port is open. If it answers with a refusal, it’s closed. If nothing comes back within four seconds, a firewall is most likely dropping the packets, which we report as no response.
Because the test comes from outside your network, it shows what the rest of the internet sees. Testing from a computer on your own Wi‑Fi using its private IP (like 192.168.1.10) would only prove the port works locally.
Port forwarding checklist
- Make sure the program (game server, Plex, camera software) is running and listening on the port.
- Give the device a fixed private IP, then forward the port on your router to that IP.
- Allow the port in the device’s own firewall (Windows Defender Firewall, for example).
- Compare your router’s WAN IP with your public IP. If they differ, or the WAN IP starts with 100.64–100.127, you are behind CGNAT and forwarding won’t work until your ISP gives you a public IP.
More help: how to check if a port is open and why port forwarding isn’t working.
Frequently asked questions
How do I check if a port is open?
Enter your public IP (filled in for you) or a hostname, pick the port and press Check. FernTool tries a real TCP connection from the internet. “Open” means something accepted the connection; “closed” means it was refused; “no response” usually means a firewall silently dropped it.
Why does my port show closed after I set up port forwarding?
The most common reasons are: the program isn’t running or listening on that port, the device’s firewall blocks it, the forward points at the wrong private IP, there are two routers (double NAT), or your ISP uses CGNAT so your router has no public IP at all.
Can I check UDP ports?
No. UDP has no connection handshake, so an outside test cannot reliably tell open from filtered. This checker tests TCP only. Game consoles and WireGuard use UDP, so test those from inside the app instead.
Is it safe to leave ports open?
Only open what you need. Every open port is a door a scanner can find. Never expose Remote Desktop (3389), databases or Telnet directly to the internet; use a VPN instead.
Why can’t I check any port I want?
To stop the tool being used for port scanning, it only checks well-known service ports, private and reserved addresses are blocked, and each visitor is limited to 10 checks a minute.