How does a web site know when the connection is using a vpn?

Websites can't see that you're using a VPN directly, but they can make a pretty good guess from a few signals: IP address lists: Most VPN servers use known IP ranges owned by VPN companies or data centres. Services keep databases of these, and sites check your IP against them. This is the most common method. Many users on one IP: If thousands of people connect from the same address, it's clearly a shared VPN server, not a home connection. Mismatched details: If your IP says Germany but your browser's time zone and language say the US, that suggests a VPN. Technical fingerprints: Some sites look at connection details, like packet size differences that VPN tunnels create, or browser leaks that reveal your real IP. That's why streaming and banking sites often detect VPNs, while most ordinary websites don't bother checking.