Mermaid is a JavaScript-based diagramming tool that renders Markdown-inspired text definitions into SVG diagrams. It supports flowcharts, sequence diagrams, ER diagrams, class diagrams, state diagrams, Gantt charts, pie charts, mindmaps, and git graphs directly inside Markdown files.
When to use: Documenting system architecture, visualizing data models, illustrating request flows, creating project timelines, embedding diagrams in GitHub/GitLab READMEs or docs sites.
When NOT to use: Pixel-perfect design mockups, interactive dashboards, diagrams requiring custom artwork or complex spatial layouts beyond hierarchical/relational structures.
Mermaid diagram syntax for flowcharts, sequence diagrams, ERDs, class diagrams, and more. Use when creating diagrams in markdown, generating architecture visuals, or documenting system flows. Use for mermaid, diagram, flowchart, sequence, ERD, class-diagram, gantt, pie-chart, mindmap. Source: oakoss/agent-skills.