A free online Mermaid diagram editor that runs 100% in your browser. Write Mermaid code and see it rendered live as crisp SVG — or switch to ASCII rendering to paste diagrams into code comments, terminals, and plain-text docs. Includes themes (Default, Neutral, Forest, Dark, Base), a template library covering flowcharts, sequence, class, state, ER, Gantt, mind maps, C4, Sankey and more, plus PNG/SVG/JPG/WebP export. No signup, no server upload — your diagrams never leave your device.

Hey Product Hunt! I built Mermaid Design because I kept needing a fast, private way to sketch diagrams while writing docs and code. Most online editors either require an account or send your data to a server — this one runs 100% in your browser: no signup, no upload, your diagrams never leave your device. What makes it different: live SVG rendering with multiple themes, plus an ASCII rendering mode so you can paste diagrams straight into code comments, terminals, and plain-text docs. There's a template library covering 20+ diagram types (flowcharts, sequence, ER, Gantt, C4, Sankey and more), and export to PNG/SVG/JPG/WebP. I'd love to hear what you think — and what diagram types or export formats you'd want next!

Mermaid Design

Free Mermaid editor with themes & ASCII rendering

Free Mermaid editor with themes & ASCII rendering