Draw sequence diagrams online with lifelines, messages and fragments
Draw a sequence diagram on Planloom’s canvas with the UML lifeline and fragment shapes from the shape library, and labelled arrows for messages. It is a drawing tool, not diagram-as-code: Mermaid sequenceDiagram source is not imported yet, but Mermaid flowcharts are, and you can export a flowchart back to Mermaid.
What you get
UML shapes built in
Lifeline, fragment, package, class and component shapes sit in the shape library, searchable with the slash tool.
Labelled messages
Draw arrows between lifelines and label each message; connectors stay attached as you reorder.
Review together
Comment on a message, discuss it live and keep the diagram beside the pull request that changes the flow.
Flowcharts as code
For process flows, paste Mermaid, edit visually and export back to Mermaid.
How it works
- 1Open a free canvas and add a lifeline for each participant.
- 2Draw labelled arrows between them in order.
- 3Wrap loops and alternatives in fragments, then share the board.
Questions
Can I write a sequence diagram as code?
Not yet. Mermaid import supports flowcharts. Sequence diagrams are drawn on the canvas.
Does it auto-lay out the messages?
No. You place lifelines and arrows yourself, with connectors that stay attached when you move them.
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Open a canvas in seconds. No account, no credit card.