So, I'll pop the question here too. I'm looking at config.tcl and how it is referenced by flow.tcl in an attempt to make it slightly more convenient to use from FuseSoC/Edalize. And out of nowhere pops up a reference to config.json. Anyone knows how it all fits together?

config.json

is an optional alternative to

config.tcl

in situations where it's not a good idea to source a tcl file (e.g., for security reasons). You can ignore it altogether if it makes your life easier.

Cool. I'll probably go with the tcl file then