MermaidViewer

About MermaidViewer

MermaidViewer is a free browser-based editor for Mermaid diagrams, aimed at developers, writers and teams who prefer typing a diagram as code over dragging boxes around. Paste or write Mermaid syntax and the diagram renders live as you type, with error messages that point to the offending line. No sign-up is needed to start.

The site supports more than 22 Mermaid diagram types, including flowcharts, sequence diagrams, ER diagrams, Gantt charts, mindmaps and C4 diagrams. An AI assistant can generate a diagram from a plain-English description, edit an existing one, explain it, or repair syntax errors. Diagrams render in the browser and autosave locally, and shareable links or embeds are available.

PNG export is included on every plan, with a watermark on the free tier. Paid Starter and Pro plans add higher-resolution and watermark-free PNG, while Pro also unlocks JPG, SVG and PDF downloads.