A recent post on HN got me thinking about how to visualize box breathing, and this is the result. I hope you'll find it useful
It can easily be installed as an app (PWA) on mobile or desktop for offline/easy access. Instructions are at the bottom of the page.
Reference post:
https://news.ycombinator.com/item?id=33586383
Source code:
https://github.com/lassebomh/box-breathing
Happy breathing HN