JASM is an assembler/disassembler for JVM bytecode. It provides a nice syntax for writing JVM classes in a bytecode-focused assembly language, and can also disassemble any Java .class file to JASM ...

Warning: blacklist/whitelist usage is recommended because this tool slows down code significantly (like do not obfuscate full Minecraft .jar) Also, this tool does not particularly obfuscate your code; ...