Because JAR files are essentially compressed archives (similar to ZIP files), you can use a file extractor to see what is inside without running any code.
A popular choice that offers a "free-to-use" trial period. It is excellent for handling JAR files and provides a clean graphical interface for browsing internal folders. Comparison of Popular Free JAR Openers Primary Use Best Feature Running applications Essential for execution 7-Zip Extracting/Viewing Open Source High compression & lightweight Jarfix Troubleshooting One-click fix for broken files PeaZip Extracting/Viewing Open Source Modern, easy UI WinRAR Extracting/Viewing Robust and familiar interface Quick Guide: How to Open a JAR File How-To Geekhttps://www.howtogeek.com How to Open JAR Files on Windows 10 and 11 - How-To Geek
If your goal is to the program contained within the JAR file (such as a game or utility), you must download the official Java Runtime Environment (JRE). Java Runtime Environment (JRE)
If you have Java installed but JAR files still won't open, Jarfix is a lightweight, free tool that restores the correct file association so they run correctly on double-click. Best Free Software to Extract or View JAR Contents