Most network troubleshooting comes down to three questions: what address am I actually using, can I reach the other end, and is the port open. Answering them usually means an RDP session to a jump host and a handful of half-remembered commands. These tools answer the same questions from a browser tab.
They run from the public internet, which is exactly what you want when the question is whether a service is reachable from outside your perimeter. For checks that must run from inside the network, the guides at the bottom cover the built-in Windows equivalents.
Tools in this category
- IP subnet calculator — network and broadcast address, usable host range, mask and CIDR conversion, and subnet splitting.
- My IP and network info — your public IP, its owner and geographic location, and what the connection looks like from the outside.
- Port Checker — test whether a TCP port on a host is open and accepting connections from the internet.
- Network diagnostics tool — reachability and latency checks against a host, in one place.
How these fit a real investigation
A service is unreachable and the firewall team says the rule is in place. Run the Port Checker against the public address first. If the port answers, the problem is inside the application or the client, not the perimeter. If it does not, you have an external test result to bring to the firewall conversation instead of an argument.
Subnet questions come up in a different context: planning a new VLAN, sizing a DHCP scope, or reading a mask in a router config that does not match what the documentation claims. The subnet calculator settles those in seconds, and the cheat sheet below is worth keeping open next to it until the maths becomes automatic.
Related guides
- How to check open ports on Windows: built-in tools vs Port Checker — when a local check answers the question and when only an external one does.
- NETSTAT command in Windows — listing listening ports and active connections, and mapping them back to a process.
- ipconfig command in Windows: beyond /all — the local view of addressing, DHCP leases and the DNS cache.
- nmap for Windows: network scanning without installing Linux — scanning a whole range when one host at a time is not enough.
- IP Subnetting Cheat Sheet — mask, CIDR and host-count reference to keep alongside the calculator.
Other tool categories
- DNS tools — record lookups, propagation, SPF and DMARC.
- Security tools — password generation and hashing.
- System tools — Windows command builders and log analysis.
- Data utilities — JSON, JWT, timestamps and cURL conversion.
- Encoding tools — Base64 and URL encoding.
- PowerShell and PowerCLI tools — vSphere command building and PowerShell guides.