Yes, but you can generate JSON with other tools easily. home.md describes how you can do it with Nix, but just as easily you can use Cue or something else.
Edit: mentioned this in the README explicitly. Thanks!
You could at least use Hujson[0], which adds comments and trailing commas; makes for a more convenient editing experience, at the price of an additional parsing step.
[0]: https://github.com/tailscale/hujson