An online port checker for one port at a time
This port checker tells you whether a TCP port on a public server or home connection can be reached from the internet. Enter a host name or IP address and a port — 22 for SSH, 443 for HTTPS, 3306 for MySQL, 25565 for a Minecraft server — and the checker tries one connection. The answer is open, closed or filtered, with what each result means and what to check next.
It is built for everyday questions: did my port forwarding work, is my game or web server reachable, did the firewall rule take effect, is my database exposed to the world? It deliberately checks one port per request and never scans ranges.
How to use the Port Checker
- Enter a host name such as
github.comor a public IP address in Host name or IP address. For your own connection, find your public IP with What Is My IP. - Type the port, or click one of the Common ports to fill it in and check straight away.
- Press Check port. Open ports usually answer in well under a second; a filtered port takes the full 6 seconds.
- Read the result and the advice under it. Every check of this visit is listed in a small table so you can compare ports and hosts.
Port Checker features
Open, closed or filtered
Open: a program accepted the connection. Closed: the host answered with a refusal. Filtered: no answer within 6 seconds, normally a firewall dropping packets.
Common ports one click away
SSH, HTTP/HTTPS, mail, SQL Server, MySQL, PostgreSQL, Redis, MongoDB, RDP, Minecraft and more, each named in the result.
Exposure warnings
Databases, caches, Telnet, FTP and remote desktops that answer from the internet get a clear warning.
Nothing sent over the connection
The checker opens the TCP connection and closes it immediately, so the service sees an empty connection and no data.
Accepts URLs and IPv6
Paste https://host:8443/path and the host and port are taken from it; IPv6 works in square brackets.
Open, closed and filtered — what to do next
Home connections behind CGNAT — common on mobile and some fibre and cable plans — share one public address among many customers, so incoming connections cannot be forwarded at all. If your router’s WAN address differs from the address What Is My IP shows, you are probably behind CGNAT.
| Result | What happened | Next step |
|---|---|---|
| Open | The TCP handshake completed | If the service should be private, restrict it with a firewall or VPN |
| Closed | The host replied with a reset (refused) | Start the program, make it listen on all interfaces rather than 127.0.0.1, or fix the forwarding target |
| Filtered | No reply within 6 seconds | Check the router’s port forwarding, the server firewall (ufw, Windows Defender Firewall, cloud security group) and whether the ISP blocks the port |
Worked example: checking a Minecraft server
A player cannot join your Java Minecraft server at home. Find your public IP with What Is My IP — say 203.0.113.7 — enter it here and click 25565 Minecraft. Filtered means the connection never reached the PC: add a port-forwarding rule on the router for TCP 25565 to the PC’s local address and allow Java through its firewall. Closed means the forwarding works but nothing is listening: start the server or check server-port in server.properties. Open means the port is fine, so look at the server address players type or at whitelist settings.
Why the test runs from the server, and why port 25 is excluded
A web page cannot open raw TCP connections, so the connection is made by this site’s checker on Cloudflare’s network. That is exactly the outside view you need for port forwarding — but it is not your device: a port can be open to the world and still blocked on your own network, or allowed from your office and filtered for everyone else. Hosts served through Cloudflare itself cannot be checked, because Cloudflare blocks raw connections to its own addresses; other CDNs answer from their edge servers, not from your origin server.
Cloudflare blocks all outgoing connections to port 25 (SMTP between mail servers) to stop spam, so it cannot be tested here; the mail ports 465 and 587 can. Only public addresses are checked — never localhost or private networks — and each network may run 30 port or certificate checks every 10 minutes. To check a site’s HTTPS certificate on an open port, use the SSL Certificate Checker.
Port Checker FAQ
How do I check if a port is open?
Enter the host name or public IP address and the port number in the port checker and press Check port. Open means a program accepted the connection; closed means the host refused it; filtered means there was no answer.
Why does my port show as filtered after I set up port forwarding?
Usually the firewall on the computer is still blocking it, the rule forwards to the wrong local IP, the program uses UDP rather than TCP, the ISP blocks the port, or the connection is behind CGNAT and cannot receive incoming connections at all.
Can I check UDP ports?
No. UDP has no handshake, so an empty probe cannot tell an open port from a filtered one. This tool tests TCP only; for UDP services such as Minecraft Bedrock (19132), test from a real client.
Why can’t I check port 25?
The check runs on Cloudflare, which blocks outgoing connections to port 25 to prevent spam. Ports 465 and 587, used by mail apps to send email, can be checked.
Is this a port scanner?
No. Each request checks exactly one port on one host and sends no data. Scanning ranges of ports on systems you do not own can break the terms of your provider.
Is it safe to check my home IP address?
Yes. The checker makes one connection to the port you choose and closes it; nothing is stored. An open port is reachable by anyone, which is why this is worth checking.