Write Mermaid.js code on the left, watch your diagram render live on the right. This free online Mermaid editor runs entirely in your browser — no login, no data uploaded to a server. It supports every Mermaid diagram type: flowchart, sequence, class, state, ER, Gantt, pie, git graph, mindmap, and user journey. How to use 1. Pick a template from the bar (Flowchart, Sequence, Class, …) or write your own Mermaid syntax in the left pane. 2. The preview updates automatically as you type (~350ms debounce). 3. Switch between four themes — Default, Forest, Dark, Neutral — to match your doc or slide. 4. Export the diagram as PNG (2× retina, dark/light background respected) or SVG (vector, ideal for docs). 5. Use the zoom controls (−/+/reset) to inspect details. Why Mermaid? It's the most widely supported text-to-diagram syntax in the developer world: GitHub renders it in markdown, Notion embeds it natively, mkdocs / docusaurus plugins read it, and most static site generators s...