Use Notepad ++
This is really comfortable to check gamedatabundle , before you need to convert the bundle in json format with some plugin ( I use JSTool )
I highly recommend writing code in Visual Studio Code (https://code.visualstudio.com/). I didn't know jack about JSON when I first starting writing POE2 mods, and I was using notepad++ then as well. However, on one of the dev tutorials here they said they were using it so I thought I'd give it a try. It runs way faster than notepad++ does, at least for me, when loading one of the big gamedatabundle files. It "prettifies" them very quickly as well. But the big bonus for me, in learning JSON, is that it automatically underlines mistaken commas, braces, and brackets for you to show you any errors in your syntax. It's helped me out a lot.
You can tell Visual Studio Code that the file you're working in is JSON by clicking in the lower right, which perhaps it will initially say "plain text" and selecting JSON. You can also make it automatically associate JSON as being the language for gamedatabundle files by going to File / Preferences / Settings and entering the following in the right side column under "User Settings":
{
"git.ignoreMissingGitWarning": true,
"files.associations": {
"*.gamedatabundle": "json"
}
}
Anyway, just my two cents. I love notepad++ as well, but using Visual Studio Code helped this JSON newbie learn quicker and recognize mistakes more easily.