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Free Online Mermaid Diagram Editor

What is Diagram-as-Code?

What is Diagram-as-Code?

Diagram-as-Code is a workflow where you define visual diagrams using plain text syntax rather than drag-and-drop GUI tools. Our editor uses Mermaid.js — a JavaScript-based tool that transforms text definitions into professional diagrams directly in your browser.

  • Text-First: Describe your diagram in plain English-like syntax instead of wrestling with GUI tools
  • Version-Control Friendly: Diagram source lives in code — easily track changes in Git alongside your project
  • Instant Preview: Live rendering with 400ms debounce so the diagram updates as you type
  • Export Ready: Download as high-resolution SVG or 2× PNG with one click

Common Use Cases

  • Software Architecture: Document microservice relationships, API flows, and system boundaries as sequence diagrams
  • Database Schemas: Visualize table relationships and entity attributes with ER diagrams
  • Git Branching: Illustrate branch strategies and merge workflows for team documentation
  • Project Timelines: Build Gantt charts for sprint planning or project management docs
  • State Machines: Model UI states, authentication flows, or system state transitions
  • README & Docs: Embed Mermaid syntax directly in GitHub READMEs which render diagrams natively

How to Use

  1. Write your diagram: Type Mermaid syntax in the left editor panel. Use Tab for indentation.
  2. See instant preview: The right panel updates in real-time as you type. Errors are shown in a non-blocking banner.
  3. Adjust the layout: Drag the divider between panels. Use Full Screen mode for a larger workspace.
  4. Zoom & Pan: Use the +/- buttons or drag the canvas to explore larger diagrams.
  5. Export: Click SVG for a lossless vector export, or PNG for a 2× high-resolution raster image.

💡 Pro Tips

  • Start with the default flowchart as a template — it shows common node types and styling
  • Use the Copy Code button to paste Mermaid syntax into README files or documentation
  • Your diagram code is auto-saved to localStorage and restored when you return
  • New to Mermaid syntax? Visit the official Mermaid documentation at https://mermaid.js.org/intro/ for a full syntax reference and tutorials

Glossary

Mermaid.js
An open-source JavaScript library that renders text-based diagram definitions into SVG/HTML visuals. Supported natively by GitHub, GitLab, Notion, and more.
Flowchart
A diagram type that represents a process or workflow using nodes (shapes) and edges (arrows). Defined in Mermaid using the graph or flowchart keyword.
Sequence Diagram
A diagram that shows how objects/services interact over time, including message passing and lifelines. Used extensively in API and microservice documentation.
Entity Relationship (ER) Diagram
A diagram that models database structure by showing entities (tables) and the relationships between them.
Gantt Chart
A horizontal bar chart representing a project schedule, showing tasks, durations, and dependencies over a timeline.
SVG (Scalable Vector Graphics)
A lossless, resolution-independent image format ideal for diagrams. Scales perfectly at any zoom level and can be opened directly in browsers.