WebRTC leak test
Press the button and your browser runs the same address discovery a video-call site would. It reports what it finds. Nothing you see here is sent anywhere, the test runs entirely in this tab.
No data leaves your browser. This test configures no STUN or TURN server, so it opens no network connection and contacts no third party. The addresses below are read locally and never transmitted or logged.
What a WebRTC leak is
WebRTC is the browser feature behind in-page voice and video calls. To connect two peers directly it must discover the network addresses each machine can be reached at, a process called ICE candidate gathering. It runs from ordinary JavaScript, without a permission prompt.
That is the problem for a VPN. A VPN works by routing your traffic through its own server, so the public address a website sees belongs to the provider, not you. But WebRTC can enumerate your addresses at the operating-system level, underneath the browser's normal request path. If it surfaces your real public IP, a page can read it directly and the tunnel is defeated, you appear to be somewhere else while quietly handing out where you actually are.
Modern browsers blunt this by returning a random *.local hostname (mDNS) in place of your real local IP, so a clean result today often shows obfuscated hostnames rather than addresses. A public address in the results is the outcome that matters: it is the classic way a VPN silently fails.