Sequence diagram generator
Map who-calls-what and in what order. Write a few lines of Mermaid and get a clean sequence diagram of your API calls, auth handshakes or message flows — rendered locally, never uploaded.
One step per line. Indent two spaces to branch beneath the line above.
Sequence diagrams make timing obvious
A sequence diagram reads top to bottom as time and left to right as participants, so it is the clearest way to document an interaction: an OAuth login, a webhook callback, a microservice call chain, or a race-prone retry. Solid arrows are requests, dashed arrows are responses, and notes call out the tricky bits.
Because each message is one line of text, the diagram stays in sync with reality — update the line, re-render, done. It belongs right in the API doc or the design RFC.
Built for design docs and PRs
Paste the Mermaid block straight into a GitHub pull request or design doc and reviewers see the flow render inline. Or export an SVG for a wiki and a PNG for a slide. Everything is generated on your device, so even an unreleased internal flow never leaves your machine.
Frequently asked questions
How do I create a sequence diagram from text?
Start with "sequenceDiagram", declare your participants, then add one message per line like "A->>B: request". The diagram renders live and you can export it as SVG or PNG.
What is the difference between a solid and dashed arrow?
A solid arrow ("->>") is a call or request; a dashed arrow ("-->>") is the response or return message. Using them consistently makes request/response pairs obvious.
Can I show alternatives, loops and notes?
Yes. Use "alt … else … end" for branches, "loop label … end" for repeated steps, and "Note over A,B: text" for annotations. See the cheatsheet above.
Is my sequence diagram uploaded?
No. It renders locally in your browser with Mermaid, so the diagram text — including internal API details — never leaves your device.
Can I auto-number the messages?
Yes — add the line "autonumber" right after "sequenceDiagram" and every message gets a sequential number, which is handy for referencing steps in a doc.