Recently one of the worst I've seen is a property management system's API: * Bugs in the implementation * JSON looks like auto-translated XML without an XML

Recently one of the worst I've seen is a property management system's API: * Bugs in the implementation * JSON looks like auto-translated XML without an XML * Nothing about data types, values for an enum you could expect On the flipside, Stripe's is one of the best. Although the only issue Ive seen is webhook signature code always uses their SDK which I don't always want to use, and webhooks can't be configured on a per-payment basis so if you have multiple systems on the same Stripe account, all of them get notified of everything (unlike other payment providers!)