Write Mermaid diagram code and see it rendered instantly. Supports 21 diagram types including flowcharts, sequence, class, state, Gantt, ER, pie, mindmap, timeline, user journey, git graph, C4 context, quadrant, XY chart, sankey, block, packet, kanban, architecture, requirement, and ZenUML. Features pan/zoom preview for large diagrams, drag-and-drop .mmd file loading, 4 themes with synced preview backgrounds, error line highlighting, PNG export with resolution options (1x-4x), and URL sharing. All rendering runs locally in your browser.