(I started this as a comment to "izzy"'s answer but due to lack of formatting options I rewrote as an answer) - Thank you @izzy for mentioning this tool)
ReText works for me as follows:
On the commandline enter retext --preview file.md
OR (to make thins easier)
I did some changes in the Python sources of the installed package (don't do this ...
I can highly recommend JSONedit. It serves as both a JSON viewer and JSON editor.
It features text, tree, and list views.
It is portable software and is free of cost (freeware). It even features a dark theme/mode.
The only issue I've had with it is that it crashes for me when I open very large (hundreds of MBs) JSON files. I'm hoping the author has time ...