Sequence Diagram Generator

Documenting API Flows with Sequence Diagrams

Sequence diagrams show how components interact over time — the order of messages between services, which component initiates each call, and what data is returned. They're the best way to document authentication flows, payment processing, webhook deliveries, and any multi-step API interaction.

With Mermaid's sequenceDiagram syntax, you define participants and message flows as text. The renderer draws the timeline automatically. A complete OAuth 2.0 authorization code flow takes about 10 lines of Mermaid syntax to document — far faster than drawing it manually.

Sequence diagrams are invaluable for onboarding (new team members understand the system faster), debugging (trace where a failure occurs in a multi-step flow), and API design reviews (catch awkward or redundant call patterns before implementation).

Tips

• Define participants at the top in the order they should appear: participant Client, participant API, participant DB.
• Use activate and deactivate to show when a service is processing — adds a visual activation bar.
• Notes: note right of API: Validates JWT here — adds inline documentation to the diagram.
• Use loop, alt, and opt blocks to show conditional and repeated behavior.