Sequence Diagram Renderer

Type a tiny Mermaid-style DSL on the left, see the SVG on the right. Participants, lifelines, solid and dashed arrows, notes, and self-messages — all rendered by hand, no Mermaid, no upload. Copy the SVG or download it as a .svg file.

Example — pick a starter — Login flow Retry with backoff Pub/sub fanout Checkout Copy SVG Download .svg

DSL quick reference

• # or // at the start of a line is a comment.
• title: Login flow — optional diagram title.
• participant Client — declare a participant. Append as Label to show a different display name.
• A -> B: message — solid arrow (synchronous).
• A --> B: reply — dashed arrow (asynchronous / reply).
• A -> A: think — self-message (loop).
• note left of A: text — note in A's left margin.
• note right of A: text — note in A's right margin.
• note over A,B: text — note spanning A and B (two or more ids).
• Indent any line by two spaces (or a tab) to continue the previous message / note body.
• Participants referenced inside messages are auto-declared; notes still require an explicit participant declaration.