APIs are important in both the organisation’s internal and external use. Organisations produce their own APIs and use the APIs of other organisations for different purposes.
You can structure API use as circles:
The inner circle contains the information system’s internal APIs, which are the most numerous and used the most.
Around this you can draw other circles: the further you move from the centre, the more limited the view the APIs offer to the information system and the further removed they are from the customer of the information system.
Updated: 8/5/2026
Internal APIs
APIs intended to be used within an information system or, more broadly, the organisation, are highly valuable. While they are usually the most common and most frequently used APIs, they are not visible outside the organisation.
Internal APIs are often technically and administratively simpler to implement than external APIs. They can be tailored to the specific needs of a particular information system.
Creating an extensive network of internal APIs will facilitate future development and make it possible to open services to external users if necessary. Different parts of the organisation can use the same, previously tested functions. For example, Amazon’s API First model has played an important role in the company's success.
Decentralised service networks and internal APIs
Internal APIs are the best way to build applications whose components have a healthy independence from each other. This gives you freedom to bring in new developers and even development teams to work on legacy applications, leading to cost savings and genuine agility.
- Juha Karvonen, Partner Solution Architect, Microsoft
Anssi Lepistö, Chief Specialist at DigiFinland Oy, brings up the fact that shared components are valuable in creating high-quality information systems and that they are impossible to implement without internal APIs.
Updated: 12/5/2026
External APIs
External APIs are used to work together with both public administration organisations and the private sector. Customer-oriented design is important when developing these APIs to make sure that they meet user needs and produce value for actors outside the organisation. To understand customer needs, it is advisable to interview and observe users.
When getting to know APIs, you should note that some people only refer to the information system's external application programming interfaces as 'APIs'. This is understandable because external APIs are required in many use cases, and their development is subject to requirements that internal APIs do not have.
Juha Karvonen, Partner Solution Architect at Microsoft, says empathically:
Using a good cloud environment is faster and easier already in the development phase than creating APIs manually or with the help of a library alone. When developing a large project, access to API prototypes will speed up and facilitate the project.
When you work from the word go in a secure environment for API publishing with an API Gateway that makes it easy to create functions, you become familiar with both the working methods and tools for the later stages of integration, testing and production.
Jari Isokallio, Chief Specialist at the Digital and Population Data Services Agency, agrees. He recommends procuring off-the-self solutions for management needs:
Using a so-called API Gateway solution is particularly important when transitioning to cloud environments. Without good practices and tools, working with cloud services quickly becomes unmanageable.
