Mermaid Diagram Editor

What Is Mermaid Diagram Editor?

Mermaid Diagram Editor is a free online tool built on Mermaid.js that lets you create diagrams and charts using simple text definitions inspired by Markdown. Instead of dragging and dropping shapes in a visual editor, you write human-readable code that describes your diagram, and the editor renders it into a polished SVG image in real time.

Mermaid has become the standard for diagrams-as-code. It is natively supported by GitHub (in Markdown files, issues, and pull requests), GitLab, Notion, Obsidian, Azure DevOps, Jira, and dozens of other tools. When you learn Mermaid syntax, you can create diagrams anywhere these platforms are used — no specialized software needed. This editor is the best place to learn, test, and preview your Mermaid code before committing it to a repository or embedding it in documentation.

The editor provides a live coding environment where you type Mermaid code on the left and instantly see the rendered diagram on the right. It supports all 20+ Mermaid diagram types, includes 11 starter templates to help you get started quickly, and offers five built-in themes to style your diagrams. When you are done, export to SVG for infinite scalability or PNG for easy sharing on Slack, email, or presentations.

All processing happens entirely in your browser. Your diagram code never leaves your device. There is no server, no account, no tracking, and no ads. This editor is part of the UseTool suite of free browser-based developer tools.

Why Use This Mermaid Editor

Speed and simplicity are the primary advantages. The page loads in under a second on mobile — the interactive editor shell weighs approximately 4 kilobytes, while the Mermaid rendering engine loads asynchronously in the background. You see the editor instantly and your first diagram renders within 1-2 seconds. Compare this to mermaid.live, which ships ~3 MB of JavaScript upfront including the Monaco editor and YAML configuration panel.

Privacy is built into the architecture. Because this is a static site with no backend server, it is technically impossible for anyone to read or store your diagrams. There are no cookies, no analytics scripts, and no third-party trackers. If you are diagramming confidential system architectures, database schemas, or internal processes, your content stays on your device.

Five built-in themes let you match your diagram to any context: Default (blue/gray) for general use, Dark for dark-mode presentations, Forest (green) for organic diagrams, Neutral (black/white) for print and documentation, and Base for custom theming. Switch with a single click — no YAML configuration needed.

Compared to draw.io (diagrams.net), this editor uses a code-based approach that is better for version control, code review, and embedding in Markdown documentation. Compared to Excalidraw, it produces structured, professional diagrams with auto-layout rather than freehand sketches. If you need diagrams-as-code, this is the fastest way to get started.

Who Is This For

Software developers use Mermaid diagrams to document API flows, system architecture, and deployment pipelines. The diagrams live alongside code in Git repositories and update with every pull request. This editor lets you preview diagrams before committing, catch syntax errors early, and export clean SVGs for README files and wikis.

Software architects and technical leads create class diagrams, state machines, and sequence diagrams to communicate system design. The ER diagram template is particularly useful for database schema design and review. Export to SVG for architecture decision records or embed in Confluence and Notion pages.

Product managers use flowcharts and user journey maps to visualize user flows, decision trees, and onboarding experiences. Gantt chart templates help plan project timelines with task dependencies. Mindmaps are ideal for brainstorming sessions and feature prioritization.

Students and educators learning UML, data structures, and database design find Mermaid's text syntax easier to learn than visual diagramming tools. Write the code, see the diagram, iterate — no mouse required. The class diagram and ER diagram templates cover the most common academic use cases.

Technical writers and documentation teams embed Mermaid diagrams directly in Markdown documentation hosted on GitHub, GitLab, or static site generators. This editor serves as a preview and testing environment — write your diagram, verify it renders correctly, then copy the code into your docs. For Markdown editing, try our Markdown Editor.

Supported Diagram Types

Mermaid supports a wide variety of diagram types. This editor includes starter templates for the 11 most commonly used types:

Supported types include: flowcharts, sequence diagrams, class diagrams, state diagrams, ER diagrams, Gantt charts, pie charts, mindmaps, timelines, user journeys, and Git graphs. Beyond these templates, the editor renders any valid Mermaid syntax automatically — including beta types like C4 context diagrams, quadrant charts, Sankey diagrams, and Kanban boards.

Mermaid Syntax Example

Here is a simple Mermaid flowchart example. Paste this into the editor above to see it rendered:

flowchart TD
    A[Start] --> B{Is it working?}
    B -->|Yes| C[Ship it!]
    B -->|No| D[Debug]
    D --> B

The keyword flowchart TD creates a top-down flowchart. Nodes are defined with ID[Label] and connections with -->. Curly braces create diamond (decision) nodes, and pipe labels -->|label| annotate connections.

Each diagram type has its own keywords and syntax patterns. Use the Template dropdown in the editor to explore working examples for all 11 supported types. The Mermaid documentation at mermaid.js.org provides the complete syntax reference.

How to Use This Editor

1. Write or paste Mermaid code in the code editor on the left. The diagram renders automatically as you type with a short delay for validation and rendering.
2. Choose a template to get started quickly. Select a diagram type from the Template dropdown — the editor loads a working starter example with key syntax patterns you can modify.
3. Pick a theme to style your diagram. Default works for general use, Dark for presentations in dark mode, Forest for organic-looking diagrams, Neutral for print, and Base for custom theming.
4. Check validation while you type. The green or red dot below the editor shows whether your syntax is valid, with the detected diagram type displayed in the status bar. If there is a syntax error, the last valid diagram is preserved while you fix it.
5. Export your diagram when ready. Click SVG for vector output (ideal for web, scaling, and editing), or PNG at 1x, 2x, or 4x resolution for sharing on Slack, email, or slides. Check "Transparent" for a PNG with no background fill. You can also copy the SVG markup or Mermaid source code directly to your clipboard.

Your code is automatically saved to your browser's local storage, so you can close the tab and come back later without losing your work. The editor supports dark mode (synced with your system preference) and adapts to mobile screens with a tabbed Code/Diagram view. Press Tab to indent with 2 spaces, and Escape to toggle between Tab insertion and standard keyboard navigation.

Mermaid Editor Comparison

There are several ways to create Mermaid diagrams online. Here is how this editor compares:

Frequently Asked Questions

Related Tools