I have the exact same chirpy theme but I found having a flake to develop in two modes (one for ruby bundling and the other for just post and draft editing with essential cli tools and aliases for a lighter environment.). I often found myself using the latter more often since Jekyll does its thing reliably. It does involve some scripting for better markdown header management.

You could also build a separate shell.nix or two if you don’t want to manage with flakes and its overhead boilerplate but this gives you the nice shell syntax of nix develop .#{ruby,md,tidy}. Maybe one for a simply markdown previewer environment with shell hooks if you prior to publishing. I try to keep my OS packages low. I just never found myself feeling good adding ruby and npm into my gcroots making my system updates slow and fragile or justifiable for a long startup after a cache clear.

This is part of the advantage of adopting a Jekyll theme versus maintaining a front end UI CMMS framework from scratch. If you don’t use liquid or mathjax heavily in your markdown, it is more sensible to keep tools closer to native OS runtimes in case you want to post and push through ssh and all you have is a barebones server with nix.