Mermaid.js
JavaScript-based diagram and charting library that renders diagrams from text definitions. Mermaid lets you write diagrams as text in Markdown-like syntax and renders them as SVG — flowcharts, sequence diagrams, class diagrams, ER diagrams, Gantt charts, Git graphs, and more. Native support in GitHub, GitLab, Confluence, Notion, and Obsidian means diagrams live alongside code in repositories. Eliminates diagram drift by treating diagrams as code.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
SVG output — sanitize input in user-facing apps to prevent SVG injection. Local rendering — no data leaves the browser. MIT licensed.
⚡ Reliability
Best When
You want to create and maintain diagrams as code in Markdown files that render automatically on GitHub/GitLab/Confluence without design tools.
Avoid When
You need interactive diagramming, precise layout control, or very complex graphs — use draw.io, D2, or Structurizr.
Use Cases
- • Create architecture and sequence diagrams as code in Markdown documentation files that render natively on GitHub without external tools
- • Generate diagrams programmatically from agent-produced structured data using Mermaid's JavaScript API for automated documentation
- • Document API flows, database schemas, and system architectures with sequence/ER diagrams that stay in version control alongside the code
- • Visualize agent workflows, decision trees, and state machines as flowcharts using Mermaid's flowchart syntax
- • Create project timeline and dependency visualization with Gantt charts in Markdown README files
Not For
- • Interactive, editable diagrams — Mermaid renders static SVG; use Excalidraw or tldraw for interactive whiteboarding
- • Complex custom diagram layouts requiring precise positioning — Mermaid auto-layouts; use draw.io or Structurizr for pixel-perfect diagrams
- • Large complex diagrams with 100+ nodes — Mermaid's auto-layout can produce poor results; use Graphviz or D2 for complex graphs
Interface
Authentication
Local library — no authentication. Mermaid.live (online editor) is free with no auth required.
Pricing
Mermaid.js library is MIT open source. Mermaid Chart (mermaidchart.com) is the commercial collaboration product by the Mermaid team.
Agent Metadata
Known Gotchas
- ⚠ Mermaid syntax varies significantly between diagram types — flowchart syntax, sequence diagram syntax, and ER diagram syntax each have completely different grammars; agents must use diagram-type-specific syntax
- ⚠ Special characters in node labels (brackets, quotes, parentheses) must be escaped or wrapped in quotes — unescaped special chars cause parse failures that show as empty diagrams
- ⚠ Mermaid rendering in GitHub/GitLab is triggered by ```mermaid code blocks — rendering in custom apps requires importing the Mermaid library and calling mermaid.render() explicitly
- ⚠ Mermaid's auto-layout algorithm (Dagre) can produce poor results for complex graphs with many crossing edges — re-ordering node definitions or using subgraphs can improve layout
- ⚠ Mermaid version compatibility in different platforms varies — GitHub uses a pinned Mermaid version; features available in the latest npm package may not render on GitHub
- ⚠ Security: Mermaid renders user-provided text as diagrams — in user-facing apps, malicious Mermaid input could inject SVG content; sanitize Mermaid input before rendering in production apps
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Mermaid.js.
Scores are editorial opinions as of 2026-03-06.