What it is

Mermaid is a JavaScript-based diagramming tool that renders diagrams from Markdown-like text definitions. It lives in the JavaScript/TypeScript ecosystem and operates both in the browser and in Node.js environments. The project’s core purpose is to eliminate the gap between software development and documentation by letting developers write diagrams alongside code, avoiding the rot and overhead of manual diagram maintenance.

Key capabilities

• Renders flowcharts, sequence diagrams, class diagrams, state diagrams, entity-relationship diagrams, user journey diagrams, and mindmaps from declarative text syntax
• Supports embedding directly in Markdown files via fenced code blocks (e.g., ```mermaid)
• Provides a live editor at mermaid.live for real-time preview and sharing
• Exposes programmatic APIs for integration into build tools, static site generators, and custom applications
• Offers configurable theming, layout options, and security settings (e.g., sanitized rendering)
• Distributes via npm, CDN, and standalone browser bundles with small gzipped footprint (~200 KB)
• Integrates with GitHub, GitLab, Obsidian, Typora, and VS Code extensions out of the box

Who uses it and how

Developers embed Mermaid in documentation repositories (e.g., READMEs, wikis) to keep diagrams synchronized with code changes. Technical writers use the Live Editor to prototype diagrams before committing them to Markdown-based docs. Teams running CI/CD pipelines generate architecture or flow diagrams programmatically as part of build steps. Researchers and educators create interactive diagrams in Jupyter notebooks or static sites using Mermaid’s JS library.

Getting started

Install via npm install mermaid or include via CDN (https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.min.js). Run mermaid.parse() or use mermaid.initialize() with a config, then call mermaid.render() to generate SVG or PNG. The Live Editor at mermaid.live provides instant no-install experimentation.

When to use it — and when not to

Mermaid replaces paid tools like Lucidchart or draw.io for text-centric workflows but lacks drag-and-drop editing or advanced layout algorithms. It requires no backend but depends on client-side JavaScript rendering or Node.js build steps. Complex diagrams may need manual tuning of layout parameters, and large-scale rendering in CI may require headless browser setup (e.g., Puppeteer). It is unsuitable for real-time collaborative editing or scenarios demanding pixel-perfect layout control.