Interfaces & APIs for financial services & banks: The key to digital transformation

The financial world is undergoing profound change. Transmissions through regulatory requirements, especially the PSD2 directive, and the increasing expectations of customers in digital, seamless experiences, have become interfaces & APIs for financial services & banks from the optional feature to existential necessity.

They are the invisible architects that enable banks and fintechs to unbundle their services, reassemble them and integrate them into the digital economy. This change concerns not only the end customer business, but also revolutionises the B2B financial services and the internal IT strategy of credit institutions.

What are APIs in the context of banks and financial services?

APIs (Application Programming Interfaces) are standardized protocols and tools that enable various software applications to communicate with each other.

In the banking sector, they have gained special significance as they regulate the secure and controlled exchange of data between financial institutions and third-party providers (Third Party Providers, TPPs).

Definition and functionality: From SOAP to REST

Short: Traditionally, communication between banking systems was often based on complex, proprietary interfaces or earlier protocols such as SOAP (Simple Object Access Protocol).

Traditionally, communication between banking systems was often based on complex, proprietary interfaces or earlier protocols such as SOAP (Simple Object Access Protocol). These were inflexible, difficult to wait and hindered the rapid development of new products.

The modern financial IT almost exclusively uses RESTful APIs (Representational State Transfer). REST APIs are lightweight, use common web standards (such as HTTP) and allow fast, scalable and secure transmission of data, usually in JSON format.

They are the backbone of Open Banking and enable banking functions such as querying an account balance or triggering a payment as modular services.

The transformation of traditional interfaces to modern APIs

The transition from rigid, monolithic systems to an agile, API-controlled architecture is a central pillar of the modernization of core banking systems. APIs decouple the user interface and external services from the complex logic in the background.

This creates an important prerequisite for innovation, as new services can be developed and provided more quickly without jeopardising the entire system.

| Feature | Traditional interfaces | Modern banking APIs (REST) | | :--- | :-- | :-- | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Protocol | Proprietary, SOAP, batch processing | HTTP/HTTPS, REST, Real-time | ** Flexibility | Low, high integration costs | High, easy connection | | Safety | Often only on network level | OAuth 2.0, tokenization, encryption | ** Innovation degree Low, focus on stability | High, basis for open banking and fintechs |

The driving forces: Why APIs are indispensable for the financial industry

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References and further reading

Short: The following independent references complement the topics in this article:

The following independent references complement the topics in this article:

• Bitkom – German digital industry association
• German Federal Office for Information Security (BSI)
• European Commission – Digital strategy
• MDN Web Docs (Mozilla)
• W3C – World Wide Web Consortium

> "AI in mid-sized companies works when processes are measurable and data is trustworthy—a pilot without a success metric is theatre." > > — Björn Groenewold, Managing Director, Groenewold IT Solutions

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