Is port 21 open?
Test whether a port on your own address answers from the internet, to check port forwarding or a server you run.
Looking up…
Open, closed, filtered.
- Open: a program on your side accepted the connection from the internet.
- Closed: your machine or router answered with a refusal; nothing listens on that port there.
- Filtered: silence. A firewall drops the attempt, the router forwards nothing, or your provider blocks the port.
Only your own address.
The checker tests the address your browser connects from, never one you type: that keeps it from being used to scan other people's networks. It tests TCP only, never port 25, and nothing is stored.
Questions people ask.
How do I check if a port is open?
Type the port number. Hivex tries to open a TCP connection to that port on the address you are connecting from, from outside your network, and says open, closed or filtered.
What is the difference between closed and filtered?
Closed: the machine answered but nothing listens on the port. Filtered: no answer at all, usually because a firewall or the router drops the connection.
Why is my port still closed after port forwarding?
The program must be running and allowed through the computer's firewall, the router must forward the port to the right local address, and your provider must not block it or share your public address (CGNAT).
Can I check a port on another address?
No. To keep the tool from being used to scan other people's networks, it only tests the address you connect from.
Can it test UDP or port 25?
No. It tests TCP only, and Cloudflare Workers, where Hivex runs, cannot open port 25.
Hivex index
Short names, still free to register.
Starting something new? Hivex keeps a live index of short, brandable .si names nobody has claimed yet, each checked with the registry.
From code, or an AI assistant.
Hivex's free JSON API and MCP server check domains, DNS and registration records from your own code or from AI assistants that speak MCP. No key needed.
More Network tools
- Ping testLatency to a site or IP: five TCP handshakes, timed.
- What is my IPYour public IP, approximate location, provider and connection.
- IP lookupOwner, network, AS number and hostname of any IP address.
- ASN lookupAS name, organisation and every prefix it announces.
- Speed testDownload, upload and latency, in the browser.
- Domain checkerIs a name free to register? Checked live on any extension.
Sources
By Hivex. Updated 10 October 2026. Records are built on the page; nothing you type is saved.