Mermaid Editor – Create & Preview Mermaid Diagrams Online
Write, edit, and live-preview Mermaid.js diagrams directly in your browser. A fast, free, and private online Mermaid editor with instant PNG and SVG export.
Free Online Mermaid Editor
FlowchartHow to Use
Free Online Mermaid Editor Overview
The ToolMono Free Online Mermaid Editor is a browser-native workspace for writing, editing, live-previewing, and exporting Mermaid.js diagrams. Edit plain-text markdown code to generate vector flowcharts, sequence diagrams, microservices architecture maps, ER diagrams, class diagrams, state machines, Gantt charts, git graphs, and pie charts with debounced live rendering, zoom/pan controls, and zero server tracking.
Updates your rendered diagram automatically 300ms after typing without requiring manual refresh clicks.
Private: Mermaid code is rendered 100% locally in your browser. Your diagram code is never transmitted to any server.
Export high-resolution scalable vector SVG files (.svg) or 2x high-DPI raster PNG images (.png).
How to Create and Edit Mermaid Diagrams Online
- Choose a Template: Select a Diagram Template (Flowchart, Sequence, Architecture, ERD, Class, State, Gantt, Git Graph, Pie Chart) or start typing in the left code editor.
- Live Debounced Preview: The right preview pane automatically re-renders vector graphics as you type.
- Zoom & Pan Controls: Use the Zoom In (+), Zoom Out (-), Reset, Fit, or Fullscreen buttons to inspect complex diagrams.
- Syntax Error Recovery: If a syntax error occurs, inspect the line number diagnostic banner to fix broken syntax without losing your work.
- Copy & Export: Click Copy Code to copy raw Mermaid markdown, or click Download SVG / Download PNG for image files.
Using Mermaid in GitHub and Markdown
Mermaid diagrams can be embedded directly into GitHub READMEs, GitLab wikis, Notion, and Markdown documentation using ```mermaid code block fences:
```mermaid
flowchart TD
A[Start] --> B[Build Application]
B --> C[Run Unit Tests]
C --> D{Tests Passed?}
D -->|Yes| E[Deploy to Production]
D -->|No| F[Notify Developer]
```Mermaid Text-Based Diagrams vs GUI Editors
Text-Based Mermaid Diagrams
- Stored as version-controlled plain text in Git repositories
- Diffable during code reviews and pull requests
- Renders automatically in GitHub and IDE markdown previews
- Zero manual alignment or dragging required
Traditional GUI Editors
- Stored as binary or proprietary XML files
- Requires manual pixel-perfect shape alignment
- Difficult to update programmatically via CI/CD
- Requires separate desktop application installations
Supported Mermaid Diagram Types
Flowcharts & Sequence
Model system logic, decision trees, API request flows, and protocol handshakes.
ER & Class Diagrams
Define database entity relationships (PK/FK) and object-oriented class hierarchies.
State & Git Graphs
Map state machine transitions, Gantt project timelines, and Git branching workflows.
Exporting Mermaid to SVG, PNG, and MMD
ToolMono exports vector SVG diagrams directly from client-side DOM rendering. PNG exports convert vector SVGs into high-DPI 2x raster images canvas rendering locally in your browser memory.
Private Local Browser Rendering & Security
100% Client-Side Privacy
Private: Mermaid code is rendered 100% locally in your web browser. Your diagram code, architecture specifications, and data schemas are never uploaded or saved to ToolMono servers.
Frequently Asked Questions
References & Standards
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