Mermaid Extensions¶

Mermaid-specific metadata should be passed with the mermaid= constructor kwarg in Python code. The data is normalized into element.extensions["mermaid"] and is consumed only by the Mermaid renderer.

from c4 import ContainerBoundary, ContainerDiagram


with ContainerDiagram("Orders") as diagram:
    with ContainerBoundary(
        "Order System",
        mermaid={"type": "System_Boundary"},
    ):
        pass

Supported fields¶

Mermaid extension support is intentionally small because Mermaid C4 has a smaller syntax surface than C4-PlantUML. PlantUML fields such as sprite, base_shape, and relationship index are not Mermaid features.

Deployment node variants¶

Mermaid supports the C4 deployment node macros Node_L and Node_R. In Python, use NodeLeft and NodeRight from c4.contrib.mermaid:

from c4 import DeploymentDiagram
from c4.contrib.mermaid import NodeLeft, NodeRight


with DeploymentDiagram("Network") as diagram:
    with NodeLeft("Public Subnet"):
        pass

    with NodeRight("Private Subnet"):
        pass

These classes are shared C4 macro helpers. They are not portable core deployment model classes, but they are supported by the Mermaid renderer and Mermaid JSON schema.