Not sure I follow. "What's in the state atom" - what do you mean by that? How r/atom works or what users of Reagent should put in their ratoms?

Well I have a r/atom with a bunch of stuff, and I'd like to formalize a bit what goes where.

What do you mean by "formalize"? Some textual description of what components should store in their state in general, same but for specific components, or maybe something that's checked at run time, maybe something else?

Using clojure.spec

Probably with add-watch then. You'd check all new values against the spec.

I am updating my state on mouse-move though, so it'd add a bunch of overhead. Maybe I'll do that during development and only check in a few key places in production.

You could throttle/debounce the check.

hmmm is there some utility for that? Or it'd be some hack with settimeout or something

https://google.github.io/closure-library/api/goog.functions.html#throttle

https://google.github.io/closure-library/api/goog.async.Debouncer.html