I started using the .gitconfig format that is similar to INI. (https://git-scm.com/docs/git-config#_configuration_file) The git program comes built in with a parser if you use the config subcommand. Everyone usually has git installed or don't mind installing it as a dependency.
$ git config ${section}.${key} ${value}
If it's a more complicated config/app then JSON and `jq` will be what I reach for.