Mermaid
Generate diagrams from text
The Lens
Mermaid turns plain text into diagrams — flowcharts, sequence diagrams, Gantt charts, ERDs, Git graphs. You type a few lines of structured text and get a diagram. It lives in your markdown files, your docs, your README.
MIT license. GitHub renders Mermaid natively in markdown files. So does Notion, Obsidian, GitLab, and dozens of other tools. Write a diagram in a code block, push it, and it shows up rendered. No image files to maintain, no external tool to open.
Everything is free. The library is MIT-licensed with no paid tier. Mermaid Chart (the commercial product from the same team) offers a visual editor and collaboration features starting at $8/user/mo, but the rendering engine and syntax are fully open source.
The catch: complex diagrams get messy fast. Once you hit 30+ nodes, the auto-layout makes questionable decisions and you can't manually position things. For polished presentation diagrams, you'll still reach for Figma or draw.io. Mermaid is best for documentation-grade diagrams that live alongside code, not boardroom slides.
Free vs Self-Hosted vs Paid
fully freeThe Mermaid library is fully open source under MIT. No paid features in the rendering engine.
**Mermaid Chart (commercial product):** - Free tier: basic editor, limited diagrams - Pro ($8/user/mo): unlimited diagrams, collaboration, export options - Enterprise: custom pricing, SSO, admin controls
Mermaid Chart is a separate product, a visual editor built on top of the open source library. You never need it. The library itself does everything through text syntax.
**Self-hosted cost:** Zero. It's a JavaScript library you include in your page, or it renders natively in GitHub/GitLab markdown.
Free. The library is MIT with zero paywalls. Mermaid Chart is an optional paid editor you don't need.
Similar Tools
About
- Stars
- 87,133
- Forks
- 8,821
Explore Further
More tools in the directory
Get tools like this delivered weekly
The Open Source Drop — the best new open source tools, analyzed. Free.