Which Java version do I need to run this JAR?

The one shown at the top: each class file records the Java release it was compiled for, and the JAR needs the newest of them. An "UnsupportedClassVersionError" when running a JAR means your Java is older than that. Newer Java runs older JARs, so installing the version shown (or later) fixes it.

Can I see the source code?

The structure, not the code: every class with its fields and methods and their types, as the javap tool shows them. Turning the compiled code back into Java source needs a decompiler such as CFR, Vineflower or JD-GUI, which run on your computer with Java.

Which Minecraft version is this mod for?

Open it here: Fabric, Quilt, Forge and NeoForge mods list what they need, usually the Minecraft version and the loader, and the page shows it under "Needs". A mod built for Fabric does not load in Forge, and the reverse; the page names which one it is.

Is my JAR file uploaded?

No. The file is read by this browser tab on your own device, and nothing is sent anywhere.

Stays on your computer How this works

Free JAR viewer: see inside a Java .jar file online

Open a .jar, .war or .ear to see which Java version it needs, its main class and manifest, its packages and the fields and methods of every class, the libraries built into it, and the details of Minecraft mods and server plugins. The file is opened in your browser and is not uploaded, and nothing in it is run.

Drop a .jar file here, or click to choose oneIt is opened by your browser, on this computer. Nothing is uploaded.

About the JAR viewer

A JAR is a Java program or library packed into one file: compiled classes, the resources they use and a manifest. Minecraft mods and server plugins are JARs too, as are web applications (.war) and enterprise ones (.ear). The question people most often have about one is simple and hard to answer without the right tools: will it run on the Java I have, and what is it?

This page reads the class files' version numbers for the Java release they need, lists the packages and classes, shows each class's fields and methods as Java's javap tool would, and reads the details mods, plugins and Maven builds leave inside. It is free to use, with no account and no upload limit, and it runs entirely in your browser: nothing is uploaded, and while the page stays open, a feature you have already used keeps working offline.

What you can see

The Java version needed to run it, from the newest class file inside, and the extra releases a multi-release JAR carries code for
The main class, the whole manifest, and the Maven group, artifact and version
Every package with its classes, and each class's fields and methods with their types
Libraries built in (shaded) or bundled (Spring Boot, WAR), with their versions
Minecraft mods (Fabric, Quilt, Forge and NeoForge) and server plugins (Bukkit, Spigot, Paper, BungeeCord, Velocity): name, version, authors and what they need
Who signed it, what the size is made of, and every file inside, each of which can be saved

How to open a JAR file

Drop the .jar file on the box above, or click the box and choose it.
The Java version, main class and any mod details appear at the top.
Open a package and click a class to see its fields and methods.

Questions

Which Java version do I need to run this JAR?: The one shown at the top: each class file records the Java release it was compiled for, and the JAR needs the newest of them. An "UnsupportedClassVersionError" when running a JAR means your Java is older than that. Newer Java runs older JARs, so installing the version shown (or later) fixes it.
Can I see the source code?: The structure, not the code: every class with its fields and methods and their types, as the javap tool shows them. Turning the compiled code back into Java source needs a decompiler such as CFR, Vineflower or JD-GUI, which run on your computer with Java.
Which Minecraft version is this mod for?: Open it here: Fabric, Quilt, Forge and NeoForge mods list what they need, usually the Minecraft version and the loader, and the page shows it under "Needs". A mod built for Fabric does not load in Forge, and the reverse; the page names which one it is.
Is my JAR file uploaded?: No. The file is read by this browser tab on your own device, and nothing is sent anywhere.

Built by John McMillan, a senior full-stack engineer. Open to remote roles: hire me.

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