In many jurisdictions, decompiling for the sake of interoperability or security research is protected, but you should always consult local laws or your legal team before proceeding with commercial products. Limitations: What Decompilers Can't Do
JD-GUI is perhaps the most classic choice. It provides a standalone graphical interface where you can drag and drop a JAR file to instantly browse its hierarchy and source code. Quick browsing and visual navigation. 2. Bytecode Viewer decompiler jar