Which tool for which problem?
Most network complaints are not a bandwidth problem. The table below maps the symptom you notice to the tool that identifies the cause.
| Symptom | Tool | Why |
|---|
| Websites load slowly, but downloads are fast | DNS Check + DNS Lookup | A slow or poorly reachable resolver delays every new connection while leaving your bandwidth untouched. |
| Some sites or services are unreachable | IPv6 Test + MTU Test | Missing IPv6 or an undersized MTU makes connections stall rather than fail with a clear error. |
| Connections drop on large files | MTU Test | With a misconfigured MTU small packets get through and large ones do not, which looks like random failure. |
| I want to know whether my VPN actually works | WebRTC Leak Test + IP Lookup | WebRTC can reveal your real IP despite an active VPN; IP Lookup shows the address the outside world sees. |
| A service on my network is unreachable from outside | Port Scanner | Shows whether the port is genuinely open on your public IP, separating router forwarding from ISP blocking. |
| Who owns this IP or domain? | WHOIS Lookup + IP Lookup | Registration data, ASN, and whether the address belongs to a datacentre or a residential connection. |
| I want to test my connection with real files | Test files | Useful for measuring a download in your own tool or terminal instead of in the browser. |
All tools work without an account and without installation. We store no results on our servers; what you measure stays in your browser.
Frequently asked questions about network tools
What is an MTU and why would I test it?
MTU stands for Maximum Transmission Unit: the largest packet your connection can send in one piece without splitting it. On ethernet 1500 bytes is typical; PPPoE connections are often 1492 and VPNs lower. If the MTU is set too high somewhere and the corresponding error message is blocked, small packets arrive and large ones do not. The result is a connection that establishes and then stalls, which is far harder to recognise than a connection that simply fails.
What is a WebRTC leak?
WebRTC is the browser technology behind video calling. To set up a direct connection your browser must know its own IP addresses, and those can be exposed to a website — even when you use a VPN, because WebRTC can operate outside the VPN tunnel. Our test opens a local WebRTC connection and shows which address surfaces. If you see your real IP while your VPN is on, your browser is leaking.
Why should I check which DNS resolver I use?
Your resolver determines how quickly domain names are turned into addresses and who can see which sites you request. By default you use your ISP's, which usually works but is rarely the fastest and not always the most private. DNS Check shows which resolver you actually use and where it sits; DNS Lookup additionally lets you inspect per record type exactly what is returned.
Is the port scanner legal to use?
On your own IP address, yes, and that is what this tool is for: verifying that a port you forwarded is genuinely open. Scanning other people's networks without permission is a different matter and may be unlawful depending on context. Use the tool only on infrastructure you are responsible for; see also our terms of use.
What is an ASN?
An Autonomous System Number identifies the network an IP address belongs to, usually an ISP, hosting provider or large organisation. It is useful for seeing whether an address belongs to a residential connection or a datacentre — handy when assessing traffic, or to check which network you yourself reach the world through.
Do these tools work on mobile?
Yes, all tools run in the browser and work on phones and tablets. Two caveats: measurements over mobile networks fluctuate more than over a fixed line, and the WebRTC test can differ per browser because browsers handle the exposure of local addresses differently.