It's generally used to check if there are leaks (IP, DNS, RTC etc) with a connection through VPN, Tor, proxy etc.
We developed it with updated state-of-the-art techniques to detect leaks.
The main page performs around 30 DNS detection tests to build a list. A single detection can be done with:
https://random_long_hash.ipleak.net/Replace random_long_hash with a random hash for every request.
You can also query any IP:
https://ipleak.net/126.96.36.199or any domain:
https://ipleak.net/nl.airvpn.orgAPI available here