tspu-probe

TSPU Probe is a native Android app, written in Russian-language documentation, that diagnoses why a VPN connection is failing on a particular network. VPN connections can be blocked at different layers of the network stack, and standard tools like ping cannot always tell you which layer is responsible. This app steps through each layer in sequence and reports exactly where the connection breaks down.

You enter a server IP address, port, and SNI (the domain name the VPN client sends when establishing a connection), and the app runs a series of tests. First it checks basic connectivity with a ping. Then it tries a raw TCP connection to see if the port is even reachable. After that it attempts a TLS handshake without specifying any domain name, then again with your specific domain. By comparing whether TLS works with and without a domain name, it can detect whether the blocking is at the TLS level or specifically triggered by a particular domain name, which is called SNI filtering.

A sweep feature runs through a list of domain names and tests each one with a short pause between tests to avoid triggering scan-detection systems. It shows which domains reach your server and which get blocked or time out, then recommends the best one to use based on connection latency.

At the end, the app gives a plain diagnosis: TCP is blocked and you should change ports, TLS is entirely blocked and you should change your server IP, SNI filtering is active and it recommends a working domain, or the network is clean and the problem is likely in your client configuration. The README is written in Russian. The app requires Android 7.0 or newer and does not need root access. It uses only standard Java and the Android SDK with no third-party networking libraries.