Which tool answers which question
Start from the problem, not the tool name. Find the question closest to yours and follow it to the right stop.
| Your question | Use | What to look for |
|---|---|---|
| What is my IP address? | My IP | Both addresses are at the top of the page, each with a copy button. |
| Is my VPN working? | My IP | Load the page with the VPN off, then on. The address and the provider should both change. If an IPv6 address from your usual provider still shows, the VPN is not carrying your IPv6 traffic. |
| Do I have IPv6? | IPv6 test | Whether your connection reaches an IPv6-only server, and which protocol your browser picks when both work. |
| Who owns this address? | IP lookup, WHOIS | IP lookup gives the provider, network number and rough location. WHOIS gives the registration record for the block the address sits in. |
| Who registered this domain? | WHOIS | The registrar, the registration and expiry dates, and the name servers. Personal contact details are usually withheld. |
| Did my DNS change go live? | DNS lookup | Compare the record with the value you set. An old value can linger until its TTL runs out. |
| Why is my email bouncing? | Blacklist check, DNS lookup, Reverse DNS | Check the sending server's address against the blocklists first. Then confirm the domain's MX and SPF records, and that the server's address has a PTR record pointing back to its hostname. |
| Is my port forward working? | Port checker | Enter your public address and the forwarded port while the program behind it is running. Open means the rule works. |
| Is the site down or is it me? | HTTP headers, Ping | Both run from our probe server, not from your connection. If the probe gets an answer and you do not, the problem is on your side. Many servers ignore ping, so for a website trust the HTTP result. |
| Where does the connection slow down? | Traceroute | A rise in delay that carries through every later hop marks where the slowdown starts. One slow hop in the middle on its own is usually harmless. |
| Is a redirect or cache header set correctly? | HTTP headers | The status code, each step of the redirect chain, and headers such as Location and Cache-Control. |
| How many addresses are in a /26? | Subnet calculator | The network address, the usable range, the mask and the host count for any prefix. |
| What does a site learn from my browser? | User agent | The user agent string your browser sends with every request, and what it says about your browser and system. |
Where each tool runs
Tools marked Runs in your browser do their work on your device. Address detection and IP lookup ask public services what they see. DNS and reverse DNS lookups go to public resolvers over DNS-over-HTTPS. WHOIS reads the registries' RDAP servers. The subnet calculator and the user agent page do not need the network at all.
Tools marked Runs from our probe server need a machine on the open internet. A web page is not allowed to send ping packets or open raw connections, and for a port check or an "is it down" test the whole point is to look from outside your network. If the probe server is not connected, these tools show sample output and label it as sample, so nothing pretends to be a live result.
The four lines
Tools are grouped by the kind of question they answer. Each line has a letter and a colour that stay the same on every page, so you always know which group you are in and which stops are next to it.
| Line | What it covers |
|---|---|
| Address | The numbers themselves: what your address is, whose address something is, whether IPv6 works, and how a network is divided into subnets. |
| Names | How names map to addresses and back, and who registered them: DNS records, PTR records and registration data. |
| Routes | Whether traffic gets there: if a host answers, which path packets take, and which ports accept a connection from outside. |
| Checks | Inspections of reputation and behaviour: spam blocklists, the headers a server sends, and what your browser announces about itself. |
New to the terms used here? The guides explain addresses and the two protocol versions in plain language.