Check if your VPN or network is leaking your real DNS resolver.
When you use a VPN, DNS queries should go through the VPN (or the VPN provider's DNS), not your ISP's resolver. A DNS leak means your device still sends DNS to your ISP or another third party, so your browsing can be logged or exposed. The DNS Leak Test performs lookups and shows which DNS servers responded; if you see your ISP's resolvers while the VPN is on, you have a leak. Use it after connecting to a VPN to verify configuration, or to check that your "DNS over VPN" or custom DNS settings are working. Fixing usually means forcing DNS through the VPN or setting the VPN client to use the provider's DNS.
Your DNS queries go to a resolver outside the VPN (e.g. ISP), so someone can see which domains you look up.
Enable "DNS through VPN" or set your device to use the VPN provider's DNS. Some clients have a "block DNS leak" option.
Run a few times; results can vary. If you consistently see non-VPN resolvers, you have a leak.
The test shows which IPs answered. If they match your chosen resolver and not your ISP, you are not leaking to ISP.
Read the tool's privacy policy. Typically the test domain is known; your other traffic is not sent to the test site.