Visual UML sequence diagram builder with automatic lifeline layout, message reordering, and vector export.
Runs in your browser
Free, no signup
UML Sequence Diagrams are the gold standard for documenting authentication lifecycles, microservice orchestrations, webhook callbacks, and multi-step API handshakes. Drawing lifelines and arrows by hand in graphic software is tedious and error-prone.
ToolDuck Sequence Diagram Maker automatically manages participant lifelines, call depths, return messages, self-invocations, and step auto-numbering. Add or reorder calls with one click, or import directly from cURL commands and Mermaid sequence syntax.
How to use this tool
1Add participants and actors (e.g. Browser Client, API Gateway, Auth Service, Database) from the left palette.
2Click "Synchronous Call", "Reply / Return", "Asynchronous Event", or "Self Call" to connect participants.
3Use the properties inspector on the right to reorder message sequences, edit labels, or toggle step auto-numbering.
4Export your sequence diagram as vector SVG, high-resolution PNG, or standard Mermaid markdown for GitHub documentation.
Frequently asked questions
Can I import a cURL command into a sequence diagram?
Yes. Use our cURL Parser tool and click "Sequence Diagram", or pass a cURL request into Diagram Studio. The engine automatically deconstructs the HTTP method, endpoint, and headers into an end-to-end API lifecycle diagram.
Does the sequence diagram maker support auto-numbering?
Yes. Step auto-numbering is built in and enabled by default, ensuring every call and response is clearly indexed for team architecture reviews.
Can I sync my diagram with Mermaid sequence diagrams?
Yes. Click "Source Code" to view the generated Mermaid syntax, or edit the Mermaid code directly to update your visual diagram with bidirectional sync.