Not a lot but it’s something. And I built the validator without even thinking about monetizing so it’s quite nice to get rewarded with some pocket money.
It’s not 100% passive, as I do spend a little time maintaining it and adding new features, but what income is 100% passive?
I think £55 a year is best case scenario. At least it likely covers web-hosting costs.
https://github.com/stripe/jquery.payment
While it's not a completely like-for-like comparison, I suspect it will be tough to justify $299 per single web site for many businesses that might use these tools in the first place. Personally, I'd want solid data about conversion rates to back up the marketing on the creditcard.js website before I'd consider spending real money on anything like this.