Plantuml Diagrams

Workflow

1. Write diagram to .puml file in project directory
2. Render with plantuml only when diagram is complete
3. Open preview with xdg-open (background process)
4. Return output file path to user

# Render PNG and open preview
plantuml -tpng diagram.puml && xdg-open diagram.png &

# Other formats
plantuml -tsvg diagram.puml   # SVG (scalable)
plantuml -tpdf diagram.puml   # PDF
plantuml -tutxt -pipe < diagram.puml  # Terminal preview (no file)

# Syntax check only (no render)
plantuml -checkonly diagram.puml

# Custom output directory
plantuml -o output_dir diagram.puml

Diagram Type Decision Tree

What are you visualizing?
│
├─ Interactions/flow between actors?
│  ├─ Time-ordered messages → Sequence
│  ├─ User goals/scenarios → Use Case
│  └─ Precise timing constraints → Timing
│
├─ System structure?
│  ├─ Code/domain model → Class
│  ├─ Object instances → Object
│  ├─ Database schema → IE/ER (crow's foot) or Chen ER
│  ├─ System components → Component
│  └─ Infrastructure/nodes → Deployment
│
├─ Behavior/process?
│  ├─ Flowchart/decisions → Activity
│  └─ State transitions → State
│
├─ Cloud/infrastructure?
│  ├─ AWS/Azure/GCP → Component + stdlib (read references/cloud-architecture.md)
│  ├─ Kubernetes → Component + K8s stdlib
│  └─ C4 model → C4 stdlib
│
├─ Planning/organization?
│  ├─ Project timeline → Gantt
│  ├─ Topic hierarchy → Mind Map
│  └─ Work breakdown → WBS
│
├─ Data visualization?
│  ├─ Network topology → nwdiag
│  └─ Config/data → JSON/YAML
│
├─ Documentation/specs?
│  ├─ UI mockup → Salt (@startsalt)
│  ├─ Grammar/syntax → EBNF (@startebnf)
│  ├─ Regex pattern → Regex (@startregex)
│  └─ ASCII art → Ditaa (@startditaa)
│
└─ Enterprise architecture?
   └─ ArchiMate model → Archimate

Quick Reference

For cloud/K8s/C4: Read references/cloud-architecture.md For extra types: Read references/extra-diagrams.md

CLI Reference

Layout Engines

Core Syntax

Sequence Diagram

@startuml
actor User
participant API
database DB

User -> API ++: POST /login
API -> DB: Query user
DB --> API: User record

alt Valid credentials
    API --> User --: 200 JWT token
else Invalid
    API --> User: 401 Unauthorized
end

note right of API: Auth service
== Later ==
User -> API: GET /data
@enduml

Participants: participant, actor, boundary, control, entity, database, collections, queue

Arrows: -> solid, --> dotted, ->x lost, <-> bidirectional, -[#red]-> colored

Activation: -> Target ++: activate, --> Source --: deactivate

Grouping: alt/else, opt, loop, par/else, break, critical, group — close with end

Notes: note left of A:, note right of A:, note over A,B:

Line breaks in notes:

• Inline note syntax (note right of A: line 1\nline 2) supports \n
• Block note syntax treats the body as literal text, so write actual line breaks instead of \n

' Inline note: \n works
note right of API: line 1\nline 2

' Block note: use real newlines
note right of API
line 1
line 2
end note

Other: autonumber, == Divider ==, ...delay..., ||| space, box "Group" ... end box

Class / ER Diagram

@startuml
class User {
  -id: int
  -name: String
  +getName(): String
  +setName(name: String): void
}

class Order {
  -orderId: int
  -total: Decimal
  +calculate(): Decimal
}

User "1" --> "*" Order : places

interface Payable <<Interface>> {
  +pay(): void
}

Order ..|> Payable
@enduml

Visibility: + public, - private, # protected, ~ package

Modifiers: {static}, {abstract}

Relationships: <|-- inheritance, <|.. realization, *-- composition, o-- aggregation, --> association, ..> dependency

Cardinality: "1" --> "*", "0..1", "1..*"

IE/ER (Crow's Foot)

@startuml
skinparam linetype ortho

entity Customer {
  * customer_id : int <<PK>>
  --
  * name : varchar
  email : varchar
}

entity Order {
  * order_id : int <<PK>>
  --
  * customer_id : int <<FK>>
  * created_at : timestamp
  total : decimal
}

Customer ||--o{ Order : places
@enduml

Cardinality: || exactly one, o| zero or one, }| one or more, o{ zero or more

Line: -- solid (identifying), .. dashed (non-identifying)

Attributes: * mandatory, <<PK>>, <<FK>>

Activity Diagram

@startuml
start
:Read input;
if (Valid?) then (yes)
  :Process data;
  fork
    :Save to DB;
  fork again
    :Send notification;
  end fork
else (no)
  :Show error;
  stop
endif
:Return result;
stop
@enduml

Actions: :text; — MUST end with ;

Conditionals: if (cond?) then (yes) ... else (no) ... endif

Switch: switch (test?) case (A) ... case (B) ... endswitch

Loops: while (cond?) ... endwhile, repeat ... repeat while (cond?)

Parallel: fork ... fork again ... end fork

Swimlanes: |Lane Name| before actions

Kill/Detach: kill (X end), detach (arrow end)

Use Case Diagram

@startuml
left to right direction

actor Customer
actor Admin

rectangle "E-Commerce" {
  usecase "Browse Products" as UC1
  usecase "Place Order" as UC2
  usecase "Manage Inventory" as UC3
}

Customer --> UC1
Customer --> UC2
Admin --> UC3
UC2 ..> UC1 : <<include>>
@enduml

Actors: actor Name, :Name: (stick figure)

Use cases: usecase "Name", (Name)

Relationships: --> association, ..> include/extend, --|> generalization

Stereotypes: <<include>>, <<extend>>

Component / Deployment

@startuml
package "Frontend" {
  [Web App]
  [Mobile App]
}

cloud "Cloud" {
  node "API Server" {
    [REST API]
    [Auth Service]
  }
  database "PostgreSQL" {
    [Users DB]
  }
}

[Web App] --> [REST API] : HTTPS
[REST API] --> [Auth Service]
[REST API] --> [Users DB]
@enduml

Components: [Name], component "Name" as alias

Interfaces: () "Name", interface Name

Grouping: package, node, folder, frame, cloud, database, rectangle, storage, queue

Timing Diagram

@startuml
robust "Web Browser" as WB
concise "Web User" as WU

@0
WU is Idle
WB is Idle

@100
WU is Waiting
WB is Processing

@300
WB is Waiting
@enduml

Participants: robust (multiple states), concise (simple states), clock

States: @<time> then <participant> is <state>

Constraints: @<time> <-> @<time> : label

Theming

@startuml
!theme spacelab
' Available: cerulean, vibrant, materia, bluegray, amiga, hacker

CLI: plantuml -theme spacelab diagram.puml

Key skinparams:

skinparam backgroundColor white  ' themes may set transparent - override explicitly
skinparam monochrome true
skinparam shadowing false
skinparam defaultFontName "Helvetica"
skinparam linetype ortho

List themes: plantuml -help shows available themes, or check https://the-lum.github.io/puml-themes-gallery/

Failure Modes

When in doubt:

• Run plantuml -checkonly before rendering
• Check the NEVER list for common mistakes
• Use skinparam linetype ortho for ER diagrams

NEVER

Syntax errors:

• NEVER forget ; at end of activity diagram actions — :text; not :text
• NEVER use @startuml for mindmap/WBS/gantt — use @startmindmap, @startwbs, @startgantt
• NEVER use end as a node/state name — reserved keyword, use End or Finish
• NEVER skip then keyword in activity if statements
• NEVER forget end to close grouping blocks (alt, loop, opt, par, etc.)
• NEVER use spaces in participant/class names without quotes — use "Long Name" as alias
• NEVER use graph keyword — PlantUML uses @startuml not graph

AWS/Cloud errors:

• NEVER use <awslib/NetworkingAndContentDelivery/...> — correct is NetworkingContentDelivery (no "And")
• NEVER use <awslib/...> without !include <awslib/AWSCommon> first
• NEVER use deprecated !define — use !$var = value

Rendering errors:

• NEVER assume crow's feet render well without skinparam linetype ortho
• NEVER render without writing to .puml file first — always write file, then render

Sequence diagram errors:

• NEVER use par/and syntax — use par/else for parallel threads
• NEVER use activate/deactivate without matching pairs
• NEVER forget to close box ... end box groups
• NEVER expect \n to render as a newline inside note ... end note blocks — use literal line breaks there

Class diagram errors:

• NEVER use extends with interface — use implements or <|..
• NEVER mix -- and - inconsistently for relationship length

Activity diagram errors:

• NEVER use if without endif
• NEVER use fork without end fork
• NEVER forget parentheses in conditions: if (condition?) then (yes)

Mind Map/WBS errors:

• NEVER use @startuml for mindmap — use @startmindmap
• NEVER use @startuml for WBS — use @startwbs
• NEVER mix + and - depth markers inconsistently in same branch

Gantt errors:

• NEVER forget Project starts YYYY-MM-DD — required for date-based tasks
• NEVER use [Task] starts [Other]'s end — correct is starts at [Other]'s end

Salt/Wireframe errors:

• NEVER use @startuml for wireframes — use @startsalt
• NEVER forget closing braces } for salt containers

Chen ER errors:

• NEVER use @startuml for Chen notation — use @startchen

EBNF/Regex errors:

• NEVER use @startuml for EBNF — use @startebnf
• NEVER use @startuml for regex — use @startregex

ALWAYS

• ALWAYS write .puml file before rendering
• ALWAYS use skinparam linetype ortho for ER/IE diagrams
• ALWAYS include AWSCommon before other AWS includes
• ALWAYS use quotes for names with spaces: "My Service" as svc
• ALWAYS end activity actions with semicolon: :action;
• ALWAYS close grouping blocks: alt/else/end, if/endif, fork/end fork
• ALWAYS use literal line breaks in block notes (note ... end note); reserve \n for inline note ... : ... syntax

Source: mgajewskik/opencode-config — distributed by TomeVault.