JavaSwan Java Decompiler

A Java bytecode toolkit written entirely in TypeScript. Read .class files, lift them to an IR, analyze them, and decompile them back to source — all without a JVM.

Note

We have a public accessible version available at https://javaswan.com.

I also wrote a blog post, would mean the world if you could read it :)

https://shanyu.juneja.net/thoughts/self-improving-decompiler/

FocuSee.Project.2026-03-05.19-16-09.mp4

Installing with NPM

Packages

Package	Description
@blkswn/java-asm	TypeScript port of OW2 ASM. Read, write, and transform raw bytecode.
@blkswn/java-ir	Intermediate representation. Lifts stack bytecode into typed expressions and a control flow graph.
@blkswn/java-analysis	Analysis framework. Class hierarchy, call graphs, constant folding, optimization passes.
@blkswn/java-decompiler	Decompiler. Turns bytecode into readable Java source.
@blkswn/java-decompiler-ai	AI cleanup pass. Renames variables, fixes formatting artifacts in decompiled output.

Apps

App	Description
similarity-eval	Benchmark harness. Scores decompiler output against original source using 9 similarity metrics.
web	Web UI. Interactive decompiler with Monaco editor.
java-format-cli	Java source formatter (Palantir). Used by the eval pipeline.
decompilers	Bundled reference decompilers (CFR, Procyon, Vineflower) for benchmarking.

How it fits together

.class / .jar file
       │
       ▼
   java-asm          read/write raw bytecode
       │
       ▼
   java-ir            lift to expressions + control flow graph
       │
       ▼
   java-analysis      resolve types, optimize, fold constants
       │
       ▼
   java-decompiler    reconstruct Java source
       │
       ▼
   java-decompiler-ai (optional) clean up variable names + formatting

Quick start

# install
bun install

# build everything
bun run build

# run tests
bun run turbo run test

Build a single package:

turbo run build --filter=@blkswn/java-asm

License

BSD-3-Clause