AI sequence diagram from description

Sequence diagrams are the sharpest tool when the story is about ordering and timing between multiple actors. Reach for them any time you need to show "who calls whom, in what order, with what response" — API integrations, authentication handshakes (OAuth, SAML, JWT refresh), distributed system message flows, database transactions with locks, WebSocket / SSE push patterns. They're the go-to for engineering docs because they force you to name each actor explicitly — you can't hand-wave "the backend does something." Every arrow has a source, a target, and a message. This makes them ideal for architecture review docs and RFCs where the reader will pick apart every interaction. A rough rule: if you find yourself saying "and then, and then, and then" more than three times in your explanation, you want a sequence diagram, not a flowchart. Sequence diagrams excel with async messages, activation bars showing when an actor is doing work, and notes annotating why a particular arrow matters. They struggle when the interaction is truly parallel with no meaningful ordering — in that case, a component diagram fits better.