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Configure class file decompilation in Katalon Studio

As a precondition before debugging test scripts, you need to prepare and attach source code to a class file in Katalon Studio.

You can read and interact with source code in previous versions by using the default feature of Eclipse Platform, Source Attachment. In version 7.9 onwards, Katalon Studio decompiles class files automatically and directly. Particularly, Katalon finds, downloads, and attaches source code behind the scene; hence, you do not have to manually perform these steps.

In case Katalon Studio fails to find the source attachment owing to the Internet connection or the jar file not being found, it decompiles a class file and displays the decompiled source.

Katalon Class Decompiler is enabled by default for all Katalon Studio instances. This document gives you many additional configurations.


  • Katalon Studio version 7.9.0 onwards.

Use Class Decompiler for debug


  • An active Katalon Studio Enterprise license
  • Katalon Studio v7.9 onwards
  • Enabled Decompiler in Katalon Preferences

With Katalon Class File Decompiler, you can always access a class file's source code to set a breakpoint for debugging test scripts. Learn about Debug Mode in Katalon Studio.


Configure Class Decompiler

For further configurations, open the Decompiler in Katalon Preferences:

  • Windows: Go to Windows > Preferences > Java > Decompiler.
  • macOS: Go to Katalon Studio > Preferences > Java > Decompiler.


Katalon Studio supports the following Decompilers, including CFR, FernFlower (selected by default), Jad-Core, JD, and Procyon.


Disable Class Decompiler

To turn off Katalon Class Decompiler, you need to set Class File Viewer to the default viewer in Preferences > General > Editors > File Associations.

  1. For "*.class" and "*.class without source" in File Types, select "Class File Viewer" in Associated Editors.
  2. Click Default to set it as the default viewer.
  3. Click Apply and Close.