plantuml

PlantUML Diagrams

Produce structurally valid PlantUML with explicit semantics and readable layout.

Routing

Choose PlantUML for UML, C4, enterprise architecture, or .puml output.
Choose the mermaid skill for lightweight diagrams embedded directly in Markdown. Install with: npx skills add full-stack-skills/document-skills --skill mermaid.
Choose the processon-diagram-generator skill when hosted editing or ProcessOn output is explicitly required. Install with: npx skills add full-stack-skills/document-skills --skill processon-diagram-generator.
Do not ask the user to choose a renderer when the requested notation or target format already determines it.

Workflow

Extract actors, components, types, states, messages, or deployment nodes from the request and source.
Select the diagram family and intended abstraction level.
Generate a complete source block with matching start/end directives.
Use aliases for long names and packages/boundaries for meaningful grouping.
Validate with a local PlantUML renderer when available; otherwise perform structural checks.
Save a .puml file only when requested or when integrating into an existing documentation tree.

Diagram selection

Need	Primary syntax
Runtime interaction	`sequence`, `participant`, `actor`
Static type model	`class`, `interface`, relationships
Logical architecture	`component`, `package`, `interface`
Runtime topology	`node`, `cloud`, `database`, `artifact`
Lifecycle	`state`, `[*]`
Workflow	`start`, `if`, `while`, `fork`, `stop`
User goals	`actor`, `usecase`
C4 model	C4 include plus `Person`, `System`, `Container`, `Component`

Load only the matching file under examples/ when syntax details are needed.

Authoring rules

Wrap standard UML diagrams in @startuml and @enduml.
Define aliases once and reuse them consistently.
Label relationships with purpose or protocol when it improves understanding.
Separate logical architecture from deployment topology when one diagram becomes crowded.
Keep C4 levels distinct; do not mix context, container, and component detail without an explicit reason.
Avoid remote !include dependencies unless the user accepts network-dependent rendering.
Do not invent components, protocols, multiplicities, or calls that are unsupported by evidence.

Output

Inline delivery:

```plantuml
@startuml
actor User
participant API
database DB
User -> API: Submit request
API -> DB: Persist data
DB --> API: Result
API --> User: Response
@enduml
```

File delivery: prefer docs/diagrams/<descriptive-name>.puml unless the repository defines another convention. Never overwrite silently.

Validation checklist

Start/end directives match.
Aliases and referenced elements are defined.
Relationship direction and multiplicity are intentional.
C4 includes are available in the target rendering environment.
No secrets or machine-specific paths appear in source.
Local rendering succeeds when a renderer is available.