JarViewer

JarViewer opens a .jar or .class file. It also opens the .zip, .tar, .7z and .gz archives that hold them. It then shows what is inside: the entry tree, class members, javap-style bytecode, the constant pool, and every class decompiled back to Java source.

It needs JavaScript, because the JavaScript is what does the work. A Web Worker inside this tab opens the zip and parses the classes. No bytes go to a server, and there is no server to send them to.