Mermaid
An open-source tool that turns short text descriptions into diagrams, including flowcharts, UML class, sequence and state diagrams, and entity relationship diagrams. GitHub renders Mermaid blocks in Markdown files, so diagrams can live next to your code in a README. It is the quickest way to keep design diagrams current.
90.4k
GitHub (mermaid-js/mermaid) · Sept 2026
Tool
Other
Mermaid
Minutes to start
All
Free
What it is
Mermaid is an open-source JavaScript tool, released under the MIT licence, that renders diagrams from a simple text syntax. You write a few lines describing classes and relationships, or messages between participants, and Mermaid draws the diagram. It supports flowcharts, sequence diagrams, class diagrams, state diagrams, entity relationship diagrams, Gantt charts and several other types. The official site has documentation for each diagram type and links to the Mermaid Live Editor, where you can type a diagram and see it update instantly.
Why it is useful for students and engineers
Software engineering and database courses ask for UML class diagrams, sequence diagrams and ER diagrams. Drawing them with a mouse is slow, and the result is an image that goes stale as soon as the code changes. With Mermaid the diagram is text, so it can live in your repository, be reviewed in pull requests and be updated in seconds. GitHub and GitLab both render Mermaid code blocks in Markdown files, so a diagram in your README appears as a picture for anyone browsing the project.
Who it is for
Anyone who needs diagrams in documentation: students writing project reports and READMEs, developers documenting a design, and teams that want architecture diagrams kept alongside code. You need no programming knowledge beyond the small syntax for each diagram type.
Getting started
Open the Live Editor from the official site, pick an example such as a class diagram, and change it. When it looks right, paste the text into a fenced code block marked mermaid in a Markdown file on GitHub. For a UML class diagram, you list classes with their attributes and methods and draw relationships such as inheritance, composition and aggregation with arrow notation. The documentation page for each diagram type lists the syntax with examples.
Limits
Mermaid chooses the layout automatically, so large diagrams can become cluttered and you have limited control over placement. For formal diagrams with precise layout, a drawing tool may still be better. For the everyday class, sequence and ER diagrams a project needs, Mermaid is usually enough.
Free or paid
Mermaid itself is free and open source. There is a separate commercial product from the Mermaid team with extra editing features; you do not need it to use Mermaid in Markdown or the Live Editor.
Common questions
Is it proper UML? It covers the common UML notations for class, sequence and state diagrams, which is what most courses and teams use. It does not implement the whole UML specification.
Can I use it in exam submissions? Check your course rules; many accept exported diagrams. The Live Editor can export images.
Ready to start?
Opens on Mermaid in a new tab.
Stuck on something specific?
Writing only gets you so far. If you want an answer to your situation rather than the general case, book a session and we will work through it together. Sessions are free for approved Sefism members, and a few slots open each week.
Follow along
New writing, resources and project ideas land here first.