jclasslib
7.1indexedVisualizes and edits Java class files and bytecode. Enables reading and writing class files, supports multiple files, offers dark mode, localizations, and an IntelliJ IDEA plugin.
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jclasslib bytecode editor and Kotlin Multiplatform class file library
Download
Installers can be downloaded from the releases section, on macOS you can install it via HomeBrew with
brew install jclasslib-bytecode-viewer
Purpose
jclasslib bytecode editor is a tool that visualizes all aspects of compiled Java class files and the contained bytecode. Many aspects of class files can be edited in the UI. In addition, it contains a Kotlin Multiplatform library that enables developers to read and write Java class files and bytecode.
Related projects
jvmguard is my other OSS project and provides JVM monitoring and production profiling with access control and audit trails. Includes a web UI, trigger-based captures, and an MCP server for AI-assisted profiling. It's quite new, so I'd be grateful for any GitHub stars 🙏
Maven repository
The Kotlin Multiplatform library to read and write JVM class files is available on Maven Central under
the coordinates: org.jclasslib:jclasslib-data:<version>.
Platform-specific artifacts are provided under
org.jclasslib:jclasslib-data-jvm:<version> and org.jclasslib:jclasslib-data-js:<version>.
jclasslib UI
In the main window of the jclasslib bytecode viewer, you can open multiple class files at the same time, by selecting class or JAR files, browsing a configured classpath or dragging class files on top of the window.
Editing
All constant pool entries can be edited. Referenced constant pool entries can directly be edited from the context menu that is shown by the "Edit" button of attributes and constant pool entries.
Bytecode instructions can be edited from the context menu:
Light mode and dark mode
By default, jclasslib uses dark mode if the system appearance is set to dark. Dark mode or light mode can be enabled persistently by selecting "File->Dark mode->On/Off" in the main menu.
Localizations
Several localizations are available and can be chosen in the UI:
IntelliJ IDEA plugin
There is a plugin for IntelliJ IDEA that can be installed via the plugin manager. The action in the "View menu" can be invoked when a Java, Groovy or Kotlin file is open in the editor.
The bytecode will be shown in the "jclasslib" tool window on the right hand side. Multiple class files can be open at the same time.
License
jclasslib bytecode editor is released under the GPL, Version 2.0.