Direct downloads for specific legacy versions like 2.5.1 are often found in the Ubiquiti Community Downloads support/utilities section Ubiquiti Community Quick Setup Guide file to your computer. If downloaded as a , unzip the contents to a folder. Right-click the file and select "Open with Java".
The Ubiquiti (UBNT) Device Discovery Tool is a legacy utility used to find and manage Ubiquiti devices on a local network. While version 2.5.1 was a popular standalone release, it has largely been superseded by more modern alternatives Ubiquiti Community Download Options ubnt discovery 2.5.1 download
This is the current recommended version. It does not require Java and runs directly in your browser. You can find it on the Chrome Web Store Legacy Desktop Tool (v2.5.1): This version is a Java-based Direct downloads for specific legacy versions like 2