Sequence diagram
A sequence diagram is a UML interaction diagram that shows how objects or actors exchange messages over time, with vertical lifelines and horizontal arrows.
In depth
Sequence diagrams are the standard way to document an API call sequence, an authentication handshake, or any interaction where the order of messages matters. The Y-axis is time (top → bottom), the X-axis is participants (lifelines), and arrows are messages with optional labels and return values.
Common patterns include synchronous calls (filled arrowhead), asynchronous calls (open arrowhead), self-calls (looping arrow back to the same lifeline), and activations (the rectangle on a lifeline that shows when an object is doing work).
OpenCharts can model sequence diagrams using its structured node types — participant, message, return, and activation — with auto-layout that keeps lifelines aligned.
Examples
- OAuth 2.0 authorization code flow
- Stripe checkout webhook flow
- MCP client → server tool call sequence
Also known as
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Build a sequence diagramRelated terms
UML
UML (Unified Modeling Language) is a standardized family of diagrams used in software engineering to model systems, including class, sequence, activity, state, and use-case diagrams.
System context diagram
A system context diagram is a high-level architecture diagram that shows a system as a single box at the center, surrounded by the people and external systems it interacts with.
User flow
A user flow is a diagram that maps the steps a user takes through a product or service to accomplish a specific goal, including screens, actions, and decision points.