What it does
Mermaid is a JavaScript diagramming tool that renders Markdown-inspired text into diagrams and charts. You can draft in the Live Editor or add the library to a web page, then keep the text definition beside the documentation it describes. It supports diagram types such as flowcharts, sequence diagrams, class diagrams, entity relationships, timelines and architecture views. This record covers the open-source Mermaid library, not the separate Mermaid Chart or Mermaid AI hosted products.
Mermaid is useful when a diagram should change along with a design note or README. A first draft can be as small as a flowchart definition in the Live Editor:
flowchart TD
Client --> API
API --> Store
For a website, the official usage guide describes installing the mermaid package and rendering diagram definitions through its JavaScript API. A team can keep the diagram source with the surrounding Markdown and regenerate the visual after changing a node or relationship. Mermaid documents flowcharts, sequence, class, state and entity-relationship diagrams, among other formats.
The syntax is intentionally more constrained than a drawing canvas, so a complicated layout may take adjustments to the text definition. The current package guide lists Node.js 22.12 or later and targets modern browser runtimes. If a page renders diagrams supplied by untrusted users, follow Mermaid's security guidance and choose configuration carefully; rendering user content in a browser deserves review rather than blind trust.
Strengths
- Diagram definitions remain editable text that can be reviewed and versioned with nearby documentation.
- The documentation covers several software-oriented diagram types, including flowcharts, sequence, class, state and entity-relationship diagrams.
Watch out for
- The JavaScript package has current Node.js and browser-runtime requirements; the Live Editor avoids local installation but does not remove the library's integration requirements.
- Public pages that render user-supplied diagram text need a deliberate security configuration.
Best for
- Keeping architecture and process diagrams beside source-controlled documentation.
- Embedding diagrams in documentation or a JavaScript application.
Sources
- Mermaid usage and JavaScript API (Oct 26, 2026)
- Mermaid user guide and getting started (Oct 26, 2026)
- mermaid-js/mermaid official repository (Oct 26, 2026)
- Mermaid MIT license (Oct 26, 2026)
- Mermaid flowchart syntax reference (Oct 26, 2026)