This is interesting. I really like the DSL. It is a little limited though, just because it works on the month-level only.

One thing that I think is missing is having different dates for transactions to occur. So like some things happen just once ever, or transactions on the last day of the month which shifts.

This just means the stats that are given by this app are a bit rough. Looking at the source it seems to estimate the projections. Not a bad thing, just something to note.

I recently translated my own script-based cash flow simulator to a web app as well, which might be interesting: https://nicktrevino.com/tools.cashflow-simulator.html

One last thing, if you haven't heard of Wails, and you like Golang, I recommend it when thinking about making a desktop version of a web app: https://wails.io/