C4/Diagram/1 - System context

• System context diagram (C4 diagram)

  • Overview

    • Level 1 static-structure view: the software system under design as one box among people (actors) and other software systems it interacts with.
    • Deliberately low detail—answers what does this system do* for whom* and what are its external collaborators**.

  • Context

    • First of the four core diagrams indexed on C4/Diagram; together with C4/Diagram/2 - Containers it is sufficient for most teams per the C4 site.
    • Corresponds to modelling the C4/Abstraction/1 - Software System boundary in its environment—not what runs inside it.

  • Key principles

    • Scope clarity — “Inside” vs “outside” the system must be obvious.
    • Audience fit — Built for non-developers and leadership as much as engineers.

  • Mechanism

    • Zoom in from here to C4/Diagram/2 - Containers to open the system and show containers.

  • Examples

    • A payments platform shown with customers, merchants, card networks, and internal admin users.

  • Misconceptions

    • “Context = deployment” — Wrong; deployment concerns belong in C4/Diagram/Deployment (supporting view).
    • “Must list every integration” — Pragmatically false; show material external dependencies only.