tools/java/bytecode viewer
// javanew

bytecode viewer

inspect jvm bytecode instructions from .class files with javap

// related tools

json → javagenerate java pojos or records from jsonjava decompilerdecompile .class and .jar files back to java sourcemaven ↔ gradleconvert dependencies between maven and gradle dsl

// about this tool

The Java bytecode viewer runs javap -verbose on your uploaded .class file and shows you the raw JVM instructions: constant pool entries, method descriptors, local variable tables, and every opcode with its operands. It is the same output you get running javap locally, available instantly in your browser without a local JDK installation.

// when to use

  • Confirm that a compiler optimization (constant folding, inlining) actually happened
  • Debug ClassFormatError or VerifyError by inspecting the bytecode directly
  • Learn how Java constructs (lambdas, try-with-resources, switch expressions) translate to JVM opcodes
  • Reverse-engineer the structure of a class file you cannot decompile cleanly

// faq

What is the difference between bytecode viewer and the decompiler?
The decompiler reconstructs high-level Java source code from bytecode — readable but an approximation. The bytecode viewer shows the exact JVM instructions stored in the .class file: opcodes (invokevirtual, aload_0, etc.), the constant pool, and stack frame information. Use the decompiler to understand what code does; use bytecode viewer to understand exactly how the JVM executes it.
Why does this require a Pro plan?
javap is a command-line JDK tool that cannot run in a browser. The .class file is sent to our server, analysed in memory, and returned. The file is never stored or logged.
// history
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