Sequence Diagram

Sequence diagrams show interactions between participants over time.

Basic Messages

sequenceDiagram
  Alice->>Bob: Hello Bob
  Bob-->>Alice: Hi Alice

Participants & Actors

sequenceDiagram
  participant S as Server
  actor U as User
  U->>S: GET /api/data
  S-->>U: 200 OK

Arrow Types

Syntax	Style
->	Solid, open head
->>	Solid, filled head
-->	Dotted, open head
-->>	Dotted, filled head
-x	Solid, cross
--x	Dotted, cross

sequenceDiagram
  A->>B: Solid arrow
  B-->>A: Dotted arrow
  A-xB: Cross

Notes

sequenceDiagram
  participant A
  participant B
  Note right of A: This is a note
  A->>B: Hello
  Note over A,B: Shared note

Loops

sequenceDiagram
  Client->>Server: Request
  loop Every 5 seconds
    Server->>Client: Heartbeat
  end

Alt / Else

sequenceDiagram
  Client->>Server: Login
  alt Valid credentials
    Server-->>Client: 200 OK
  else Invalid
    Server-->>Client: 401 Unauthorized
  end

Full Example

sequenceDiagram
  actor User
  participant App
  participant API
  participant DB

  User->>App: Click submit
  App->>API: POST /orders
  API->>DB: INSERT order
  DB-->>API: OK
  API-->>App: 201 Created
  App-->>User: Show confirmation