C4modell

The C4 model, also known as the C4Modell in German contexts, is a framework for describing software architecture through a small set of hierarchical diagrams. It was created to provide a simple, scalable way to communicate architecture to a wide range of stakeholders. The model centers on four levels of abstraction: System Context, Containers, Components, and Code.

System Context diagrams depict the software system as a box within its environment, showing users, external systems, and how the system interacts with them. Container diagrams break the system down into high-level containers, such as web applications, mobile apps, databases, and services, and describe their responsibilities, relationships, and technology choices. Component diagrams zoom into each container to reveal its internal components, their interfaces, and dependencies. Code diagrams, which are optional, illustrate the internal structure of a component, mapping to source code elements like classes or packages.

The C4 model emphasizes clarity and consistency, avoiding excessive detail at higher levels while allowing deeper insight where needed. It remains technology-neutral and can be used with various notations and tools. Common tooling includes Structurizr and PlantUML, and the diagrams are often produced in lightweight, readable formats suitable for both technical and non-technical audiences. While the C4 diagrams resemble some UML concepts, the approach deliberately uses simple box-and-arrow visuals and a plain naming convention to reduce cognitive load.

Origins of the model are attributed to Simon Brown, who introduced it to provide a pragmatic alternative to traditional UML-based architectural documentation. Since its inception, the C4 model has gained broad adoption in industry and academia as a method for documenting and communicating software architecture at multiple levels of detail.