magnus919_agent-skills/mermaid-diagrams/references/sequence.md

Sequence Diagrams

Best for: interaction protocols, API call flows, agent handoffs, multi-service communication.

Basic Syntax

sequenceDiagram
  participant A as Service A
  participant B as Service B

  A->>B: Request
  B-->>A: Response

Participant Types (v11+)

sequenceDiagram
  participant A as 🧑 User
  participant G as ⚙️ API Gateway
  participant B as 🕸️ Browser
  database D as 📦 Database
  actor E as 🌐 External

  A->>G: scrape(url)
  G->>B: render(url)
  B->>D: cache result
  B-->>A: markdown

Loops and Conditions

sequenceDiagram
  participant A as Agent
  participant S as Search-Svc

  loop Until goal satisfied
    A->>S: search(query)
    S-->>A: results
    alt results sufficient
      A->>S: stop
    else need more
      A->>S: refine query
    end
  end

Activation (Lifecycle)

sequenceDiagram
  participant A as A
  participant B as B

  activate A
  A->>B: Request
  activate B
  B-->>A: Response
  deactivate B
  deactivate A

Critical Rules

• activate/deactivate must be balanced
• alt/else/end for conditional branches
• loop/end for iterations
• par/and/end for parallel
• break/end for exit conditions
• critical/option/end for critical sections