Test for DNS leaks that might reveal your browsing activity to your ISP despite using a VPN or proxy.
DNS Leak Tester checks which recursive DNS service appears to handle name lookups from the current browser session. It triggers lookups for test hostnames and reports the resolver addresses observed for those requests. Compare those addresses with the DNS service expected from your VPN, proxy, browser secure-DNS setting, or local network. A common surprise is that a displayed address normally identifies a DNS resolver, not the browser's public IP address and not necessarily the user's physical location.
During a run, the browser resolves one or more test names. Those requests follow the DNS path active for that browsing context, which may involve operating-system DNS, VPN-provided DNS, browser-managed encrypted DNS, or another configured resolver. The tester reports the resolver addresses associated with the resulting lookups.
Interpretation depends on the intended setup. With a VPN connected, expected results might belong to the VPN provider or to a DNS service deliberately selected by the user. An ISP-operated resolver can indicate that lookups are leaving the intended tunnel. Multiple resolvers may also be legitimate because of redundancy, split DNS, or browser-specific settings.
There is no provider-independent list. If the goal is to use a VPN's DNS, an address associated with the ISP is suspicious, while the VPN's documented resolver or a deliberately configured third-party resolver may be expected. Compare the result with the intended DNS setup. An unfamiliar location alone is not enough to establish a leak.
DNS clients and services may use several resolvers for availability, route different names through different paths, or combine browser-managed DNS with system settings. Multiple entries do not by themselves prove a leak. Check whether every listed operator is expected, then repeat the test after reconnecting the VPN or changing one DNS setting at a time.
The behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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