mermaidjs

Use when creating text-based diagrams that render in Markdown environments. Mermaid.js is the most widely supported diagrams-as-code tool, with native rendering in GitHub, GitLab, Notion, and many documentation platforms. USE FOR: flowcharts, sequence diagrams, class diagrams, state diagrams, ER diagrams, Gantt charts, pie charts, mindmaps, timelines, git graphs, quadrant charts, C4 diagrams in Markdown, diagrams embedded in PRs and wikis, GitHub-native diagram rendering DO NOT USE FOR: enterprise architecture (use togaf or archimate), C4-specific DSL tooling (use c4-diagrams), advanced layout control (use d2)