sequence-diagram

Update Sequence Diagram

When to use this skill

Use this skill when creating a new Mermaid sequence diagram or updating an existing one. This covers syntax for participants, messages, activations, notes, loops, alternative paths, and parallel actions.

Instructions

1. Start with sequenceDiagram: Every sequence diagram must start with this keyword.
2. Define Participants (Optional):
   • Implicit: Alice->>Bob: Hello John, how are you?
   • Explicit: participant Alice or participant A as Alice
   • Participant Types:
     • actor Alice (Stick figure)
     • participant Alice @{ "type": "boundary" }
     • participant Alice @{ "type": "control" }
     • participant Alice @{ "type": "entity" }
     • participant Alice @{ "type": "database" }
     • participant Alice @{ "type": "collections" }
     • participant Alice @{ "type": "queue" }
     • Note: Do not use as alias and @{ "type": ... } simultaneously.
3. Actor Creation and Destruction:
   • Create: Add create participant <Name> before the message that creates it.

     create participant B
     A->>B: Hello
     

   • Destroy: Add destroy <Name> before the message that destroys it.

     destroy B
     A->>B: Delete
     

4. Use Correct Message Syntax:
   • -> Solid line without arrow
   • --> Dotted line without arrow
   • ->> Solid line with arrowhead
   • -->> Dotted line with arrowhead
   • -x Solid line with a cross at the end
   • --x Dotted line with a cross at the end
   • -) Solid line with an open arrow at the end (async)
   • --) Dotted line with an open arrow at the end (async)
5. Manage Activations:
   • Explicit: activate Alice ... deactivate Alice
   • Shorthand: Alice->>+Bob: Hello (activate Bob), Bob-->>-Alice: Hi (deactivate Bob)
6. Add Notes:
   • Note right of Alice: Text
   • Note left of Alice: Text
   • Note over Alice: Text
   • Note over Alice,Bob: Text spanning both
7. Control Flow:
   • Loop: loop Loop text ... end
   • Alt: alt Describing text ... else ... end
   • Opt: opt Describing text ... end
   • Par: par [Action 1] ... and [Action 2] ... end
   • Critical: critical [Action] ... option [Circumstance] ... end
   • Break: break [something happened] ... end
8. Multi-line Text: Use <br/> instead of \n for line breaks in messages and notes.
9. Background Highlighting:
   • rect rgb(0, 255, 0) ... end
   • rect rgba(0, 0, 255, .1) ... end
10. Sequence Numbers:
    • Add autonumber to the beginning of the diagram to automatically number messages.

Example

sequenceDiagram
    autonumber
    actor U as User
    participant C as Client
    participant S@{ "type": "control" }
    participant Database@{ "type": "database" }

    U->>C: Request Data
    activate C
    create participant T as Task
    C->>T: Start Task
    T-->>C: Task Started
    destroy T
    C->>T: Stop Task

    C->>S: API Call
    activate S
    S->>Database: Query
    activate Database
    Database-->>S: Result
    deactivate Database
    S-->>C: Response
    deactivate S
    C-->>U: Display Data
    deactivate C