Mermaid Diagram Generator

What This Mermaid Diagram Generator Does

Mermaid is a text-based diagramming language. Instead of dragging boxes around a canvas, you describe a diagram in short lines of markup, and a renderer draws it for you. This generator pairs a syntax editor with a live preview, so you can type on the left and watch the diagram redraw on the right. When it looks right, export it as an SVG for crisp scaling or a PNG for sharing.

Nine diagram types ship with templates: flowcharts, sequence diagrams, class diagrams, state diagrams, ER diagrams, Gantt charts, pie charts, git graphs, and mind maps. Pick a template from the dropdown, replace the sample content with your own, and the preview keeps up as you type. If the syntax breaks, a readable error appears instead of a blank panel.

How to Use It

1. Choose a template from the Load Template dropdown. The editor fills with working Mermaid syntax for that diagram type.
2. Edit the text. Node names go in square brackets, arrows are drawn with dashes and angle brackets, and labels follow a colon. The preview re-renders about a third of a second after you stop typing.
3. Fix any errors the preview reports. Mermaid errors usually name the line where parsing stopped, which is almost always one line above the real problem.
4. Export with Copy SVG, Download SVG, or Download PNG. SVG is best for documents, docs sites, and further editing. PNG is best for chat, slides, and anywhere SVG is not accepted.

Diagram Types and When to Use Each

Flowcharts explain processes and decision paths: onboarding steps, support triage, approval chains. Sequence diagrams show messages between systems over time, which makes them the right choice for API calls and multi-step transactions. Class diagrams model types and their relationships for object oriented design. State diagrams capture the lifecycle of a single entity, such as an order moving from draft to review to published.

ER diagrams map database tables and their keys, and render well in technical specs. Gantt charts lay out project schedules, dependencies, and milestones. Pie charts summarize proportions at a glance. Git graphs visualize branches and merges, and mind maps work well as brainstorming summaries that later turn into structured docs.

Mermaid Syntax Basics

Every diagram starts with a keyword that declares its type, such as flowchart TD for a top-down flowchart or sequenceDiagram for a sequence. In flowcharts, A[Start] defines a node with the label Start, an arrow is written as -->, and {Question?} creates a decision diamond. Subgraphs group related nodes, and styling directives such as classDef let you color nodes by category.

Indentation matters less than in Python, but keeping one statement per line makes errors easier to find. Comments start with %%. When something fails, simplify: comment out half the diagram and see which half still renders.

Exporting Diagrams

Download SVG when the diagram will be embedded in a page, a README, or a slide deck that supports vector graphics. SVG stays sharp at any zoom level and the file is small. Download PNG when you need a fixed image for a chat message, a ticket, or a service that only accepts raster formats. The exporter rasterizes at twice the natural size and paints a white background, so text stays legible when the image is scaled.

Copy SVG puts the raw markup on your clipboard, ready to paste into an HTML file or inline it in a template. Because the markup is just text, the diagram is also version control friendly: diffs show exactly which node or label changed.

Why Text-Based Diagrams Age Better

A diagram drawn in a visual editor often becomes stale because updating one box means reopening the file and finding the right tool. A Mermaid block lives next to the code or document it describes. It survives renames, gets reviewed in pull requests, and regenerates identically for every reader. That is why GitHub, GitLab, and many documentation platforms render Mermaid natively in Markdown fences.

Related Tools

If you are documenting a project, pair this with the Live Markdown Editor for prose that includes Mermaid blocks, the JSON Formatter for cleaning up API payloads you diagram, and the SVG Path Optimizer to slim exported vector files.