Bunq

Bunq's API is exceptional among banking APIs, being the world's first fully open banking API.

OAuth2 and API key authentication are well-implemented, with comprehensive SDKs and documentation. The API covers complete banking functionality including accounts, payments, cards, and business banking. Real-time webhooks and extensive automation features set it apart from traditional banks. However, it requires a Bunq account and understanding of banking concepts. The API complexity matches its powerful feature set.

It's ideal for fintech applications and financial automation, particularly strong in European markets with innovative features like ethical investment choices.