I would like to write my own read-only client(s) to pull my transactions from the bank and keep track of my spending. It would be possible to then feed this into other software (either that I write myself or that I can find and trust).
In the future, the goal is to actually initiate transfers to European bank accounts. For example an automatic transfer between savings accounts when the interest rates increase for one bank, or transfer from a savings account to a stock exchange instead of letting it sit on a stock exchange waiting to be invested.
It’s not entirely clear where to start as the banking system seems quite opaque and it feels like I’d have to get a job at the bank to understand how it works. Stock and crypto exchanges have APIs and sometimes even libraries, but banks?
Edit: no libs, but PSD2 is the keyword. Banks in the EU must(?) support open banking and provide APIs following that standard.
There are lots of SaaS products out there which will let you do this.
Is it a good idea? No - there will be little if any recourse if your software deletes your money. It simply isn’t worth the risk.
I recommend using yourself as the API. You can write a script which scrapes data about interest rates etc and notifies you when a transaction should be made.