Download JD-GUI to open JAR file and explore Java source code file (.class .java)
Click menu "File → Open File..." or just drag-and-drop the JAR file in the JD-GUI window scrooge-sbt-plugin_2.10_0.13-3.17.0-fda97c3c64755e87643b4700e3b9ac136f24e79d.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.