How to read the result
When you'd use this
The most common reason is testing a port-forward. You've forwarded a port on your router to a device at home, and you need to know if the outside world can actually reach it — something you can't verify from inside your own network, because local traffic never leaves it.
It's the go-to check for self-hosted services: confirming a Home Assistant instance, a Plex or Jellyfin server, a game server, or a NAS is reachable before you hand out the address. If a remote connection is failing, this tells you in one step whether the problem is your network edge or something further in.
A note on CGNAT
If a port reads filtered no matter what you forward, your provider may put you behind carrier-grade NAT — you share one public IP with many customers and can't accept inbound connections at all. In that case a forward can't help; you'd need a static IP from your ISP, or a tunnel like Cloudflare Tunnel or Tailscale.
Frequently asked questions
My service is running but the port shows closed. Why?
What's the difference between closed and filtered?
Can I check a port on someone else's IP?
Does a closed port mean I'm secure?
Live tool. This runs a real connection attempt from the edge back to your IP and returns open / closed / filtered plus round-trip time. FAQ ships as FAQPage schema; page carries SoftwareApplication + BreadcrumbList.