Java Class File Viewer | Online Bytecode Viewer

Java class file viewer for .class and .jar files: javap -c style bytecode, the constant pool and the Java version each class targets. In-browser, free.

Also known as: java class file viewer · class file viewer online · java bytecode viewer online · javap online · view class file online · java class version checker · check java version of class file · jar file viewer online · class file reader online · java disassembler online

developer utilities

encoding and decoding tools

viewers

Class or JAR File

Drop a .class or .jar file here, or click to browse

Parsed in your browser and never uploaded. JAR, WAR and EAR archives list every class inside them.

Class File Output

The disassembled bytecode, constant pool and class summary will appear here. Open a .class or .jar file, or click Load Example.

About the Java Class File Viewer

This viewer opens compiled Java .class files and JAR archives and shows what is inside: the bytecode of every method in the same layout as javap -c -p, the full constant pool as javap -v prints it, and a summary with the Java version the class was compiled for. It parses the bytes in your browser, so nothing is uploaded and you do not need a JDK installed.

Key Features

Bytecode disassembly that matches javap -c -p line for line, including tableswitch, invokedynamic and exception tables
Constant pool view in javap -v format with resolved method, field and string references
Java version detection from the class file major version, from Java 1.1 through Java 25 and preview builds
Opens JAR, WAR and EAR archives, lists every class and counts classes per Java version
Generic signatures, records, enums, sealed types and module-info.class descriptors
Copy or download any view as plain text

Use Cases

Find out which Java version a dependency JAR was compiled for before a Java 17 to Java 21 upgrade
Debug an UnsupportedClassVersionError on a Jenkins or GitHub Actions build agent
Check how javac compiled a switch, a lambda or a string concatenation while tuning hot code
Inspect a class from a vendor SDK when you have the JAR but no source
Teach JVM bytecode in a Java course without asking students to install a JDK

Supported Formats

.class (Java 1.1 to 25)

.jar

.war

.ear

module-info.class

Related Keywords

java class file viewer

class file viewer online

java bytecode viewer online

javap online

view class file online

java class version checker

check java version of class file

jar file viewer online

class file reader online

java disassembler online

How do I check which Java version a class file was compiled for?

Bytes 7 and 8 of every class file hold its major version, and the Java release is that number minus 44: 52 is Java 8, 61 is Java 17, 65 is Java 21 and 69 is Java 25. A JVM refuses classes newer than itself with UnsupportedClassVersionError. On the command line, javap -v MyClass.class | grep major prints it; this viewer shows it for a single class and counts every class in a JAR, which catches the one library compiled for a newer release than your runtime.

Privacy & Security

All processing happens locally in your browser. Your data never leaves your computer, ensuring complete privacy and security.

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Frequently asked questions

What is Java Class File Viewer used for?

Java class file viewer for .class and .jar files: javap -c style bytecode, the constant pool and the Java version each class targets. In-browser, free.

Is Java Class File Viewer free to use?

Yes. Java Class File Viewer is completely free with no usage limits, and there is no paid tier required to use it.

Do I need an account to use Java Class File Viewer?

No. Java Class File Viewer works immediately in your browser with no signup, login, or email address required.

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