PlantUML Relationship and Layout Helpers¶

Directional relationships, bidirectional relationships, and relative layout helpers are PlantUML-only convenience DSL. Import them from c4.contrib.plantuml; they are not portable C4 model data.

Relationship helpers¶

from c4 import Container, ContainerDiagram, Person
from c4.contrib.plantuml import BiRelRight, RelDown, RelRight


with ContainerDiagram("Orders") as diagram:
    customer = Person("Customer")
    web = Container("Web App", "Accepts customer traffic", technology="React")
    api = Container("Orders API", "Handles order requests", technology="Python")
    worker = Container("Worker", "Processes async jobs", technology="Python")

    customer >> RelRight("Uses") >> web
    web >> BiRelRight("Calls") >> api
    api >> RelDown("Publishes jobs") >> worker

Available relationship helpers:

Direction or behavior	Helpers
Backward	`RelBack`
Neighbor	`RelNeighbor`, `RelBackNeighbor`
Down	`RelD`, `RelDown`, `BiRelD`, `BiRelDown`
Up	`RelU`, `RelUp`, `BiRelU`, `BiRelUp`
Left	`RelL`, `RelLeft`, `BiRelL`, `BiRelLeft`
Right	`RelR`, `RelRight`, `BiRelR`, `BiRelRight`
Bidirectional generic	`BiRel`, `BiRelNeighbor`

Relative layout helpers¶

Layout helpers map to C4-PlantUML Lay_* macros and constrain where one element is placed relative to another.

from c4 import Container, ContainerDiagram
from c4.contrib.plantuml import LayRight


with ContainerDiagram("Orders") as diagram:
    api = Container("Orders API")
    database = Container("Orders DB")

    LayRight(database, api)

Available layout helpers:

Position	Helpers
Down	`LayD`, `LayDown`
Up	`LayU`, `LayUp`
Right	`LayR`, `LayRight`
Left	`LayL`, `LayLeft`

Use diagram-level render options such as layout_top_down() or layout_left_right() for the broad direction of the diagram, and use Lay* helpers only when a specific relative placement matters.