A financial API is an application programming interface that gives other software access to financial data or services, such as account balances, transaction histories, payments, card issuing, identity checks or market prices. The general idea, how requests and responses work and how APIs are secured, is explained in full in the Application Programming Interface (API) entry.
Financial APIs come from many kinds of provider. A bank may publish a bank API for its own accounts, sometimes because open banking rules require it. A payment gateway offers APIs that let a website accept cards and wallets. Platforms selling banking-as-a-service use APIs to let non-banks open accounts and issue cards, and market-data firms sell price feeds the same way.
Because financial APIs can move money or expose personal data, they normally require strong authentication, encryption and careful limits on what each connected app is allowed to do.