Networking Tool · Retired

Port Check

A port check tells you whether a TCP port on a host accepts connections from outside your network — useful when you're debugging firewall rules, testing whether your home router has forwarded a port, or sanity-checking that a freshly deployed service is actually listening. Here's how to do it today.

From the command line

Use nc (netcat) — every Unix-like system ships with it:

nc -zv example.com 443           # check port 443 (TLS)
nc -zv example.com 22 25 80 443  # check several at once
nc -zv -w 3 example.com 8080     # 3-second timeout

Or use nmap for a more thorough scan (with permission — port-scanning hosts you don't own can be considered hostile in some jurisdictions):

nmap -p 22,80,443 example.com    # specific ports
nmap -p 1-1024 example.com       # well-known port range

On Windows, Test-NetConnection is the equivalent:

Test-NetConnection example.com -Port 443

From a browser

Browsers can't open arbitrary TCP sockets, but services like check-host.net and yougetsignal.com run port checks from external probes — handy when you need to confirm a port is open from the public internet, not just from your own network.

Why we retired it

Cloudflare Workers do support outbound TCP via the cloudflare:sockets API, so a port-check tool is technically possible — but a single-location probe from the nearest Cloudflare edge isn't much more reliable than just running nc on your own machine, and the established multi-region services above already do this well.

If you'd find a single-location probe useful here, let us know — it's a couple of hours' work to bring it back.

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