The browser

WebRTC leaks and timezone mismatches

WebRTC is how browsers do voice and video calls. While setting up a call it gathers “ICE candidates”: possible network paths, including local addresses. A VPN is supposed to be the only public address a site sees. A leak is a second public address, gathered by the browser, that is not the VPN address.

What the test on this site does

It runs only after you click. It opens a peer connection, asks a public STUN server for candidates, and compares them with the IP this site already saw. A 10.x, 192.168.x, or 100.64.x address is your own network or CGNAT, not a leak by itself. An mDNS name such as abc.local means the browser hid the local address, which is what current browsers try to do.

Timezone

The browser timezone comes from the operating system. The IP timezone comes from a geolocation database. They differ when you travel, when the database is wrong, and when a VPN exits in another region. A mismatch is a reason to look, not proof of a VPN. Pair it with the location checker and the ASN on the privacy check.