Free Mermaid Diagram Editor

Type Mermaid syntax on one side, watch the diagram redraw on the other. The editor covers flowcharts, sequence diagrams, ER diagrams, class diagrams, mind maps, and Gantt charts, which is most of what a technical document ends up needing. Finished work exports as SVG or PNG. Nothing gets installed and no plugin has to be wired into a documentation toolchain; the page is the tool. There is no account to create and no charge to use it.