I want a to-do list app that syncs from a json file (or other human-readable data format), so that I can view and modify the file (via a CLI like jq) from my computer too, and it would still reflect on my phone when it syncs.
Does this exist? Preferably it uses a format simple enough that makes it possible / easy to modify it via jq.
Not exactly what you asked for but Joplin files are markdown. The app itself (very cross platform) renders them in a nice format. https://joplinapp.org/