If you invoice or onboard Polish companies, sooner or later you have to check two dull things that turn out to matter a lot: is this company actually a registered VAT payer, and is the bank account they gave you the one that's on the government's official white list ("Biała Lista")? Both of those affect whether you can deduct the cost and reclaim VAT, so it's not really optional.
The annoying part is that the data lives in four different places: the Ministry of Finance, the KRS court register, GUS (the stats office), and the EU's VIES service. Each one has its own API and its own quirks.
I got tired of gluing those together every time, so I wrapped them behind a few plain HTTP calls that return JSON. Full disclosure: skanfirmy.pl is mine. It's free, no key, no signup, and the web layer runs client-side with no tracking. Here's how you'd actually use it.
REST: one GET, one JSON
Cheapest thing you can do is check a NIP (the tax ID):
