Mermaid
Text syntax to generate diagrams (flowchart, sequence, class, ERD, gantt, state) right inside Markdown. Native rendering on GitHub, GitLab, Notion, Obsidian.
Strengths
- Diagrams-as-code: versioned in Git, readable diff, refactor by search/replace
- Native GitHub README rendering, a diagram in a commit, visible instantly
- Easy LLM generation: Claude/GPT produce correct Mermaid without config
- Open-source, active community (300+ contributors)
Limitations
- Auto layout not always ideal, for complex diagrams, draw.io is still better
- No visual editing, you write the syntax (but AI helps)
- For UX diagrams (wireframes), Figma is still the tool
Best for
- Architecture diagrams living in the repo (README.md, docs/)
- DB schema ERDs documented next to migrations
- API or auth flow sequence diagrams generated by LLM