[rafram]

Things may have changed, but my impression as of several years ago was that JD-GUI was far, far behind the state of the art (Fernflower, aka the built-in IntelliJ decompiler) in terms of correctness, re-sugaring, support for modern Java features, and so on. Fernflower is open source as part of IntelliJ: https://github.com/fesh0r/fernflower

[GranPC]

Is there a good GUI for this a la jadx-gui that isn't an entire IDE?

[rafram]

Not that I know of. The features I'd want in order to consider a decompiler GUI "good" (e.g. a good text editing control, go-to-definition, find usages, manual renaming of obfuscated symbol names) quickly approach the scope of an entire IDE, though.

[DefineOutside]

The most feature advanced decompiler I know of is Recaf. It supports a mix of decompilers and even bytecode editing.

[GranPC]

This looks excellent. I'll be sure to try it out. Thanks!

[mudkipdev]

Recaf