Seq Diagram

I got tired of opening Lucidchart or draw.io every time I needed a quick sequence diagram — fighting with boxes and arrows for something that should take two minutes. SeqDiagram is the alternative: you just write the flow as text, and the diagram appears on the right as you type.

The syntax is minimal. Browser->Server: POST /login, Server-->Browser: JWT token — that's it, you're halfway done. It handles participants, actors, async messages, loops, alt/else blocks, activation bars, notes. Everything a proper UML sequence diagram needs, nothing you have to click into existence.

When you're done: share it with a link (the whole diagram is encoded in the URL, no backend), download as PNG or SVG, or export to Mermaid so it lives in your GitHub README or Notion doc. There's also a Copy Image button that puts it straight on your clipboard — paste directly into Slack or a PR comment.

Free. No sign up. Works in the browser. Your diagrams autosave locally and stay private.

Good alternative to Lucidchart, draw.io, Mermaid Live Editor, PlantUML, and WebSequenceDiagrams if you want something that just gets out of the way.