Mermaid Render

mermaid-mcp

An MCP server that renders Mermaid diagrams to PNG or SVG. Give your LLM the ability to turn diagram syntax into actual images.

Quick start

Claude Code

claude mcp add mermaid -- npx -y mermaid-render-mcp

Claude Desktop

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "mermaid": {
      "command": "npx",
      "args": ["-y", "mermaid-render-mcp"]
    }
  }
}

Note: the first run downloads headless Chromium (~150 MB), so the initial startup takes a few minutes.

From source

git clone https://github.com/tci-nebula/mermaid-mcp.git
cd mermaid-mcp
npm install
claude mcp add mermaid -- node /path/to/mermaid-mcp/server.js

Tool: render_diagram

Parameter	Type	Default	Description
syntax	string	(required)	Mermaid diagram definition
format	png | svg	png	Output format
theme	default | dark | neutral | forest	default	Visual theme
background	string	white	CSS colour or transparent
width	number	1200	Canvas width in px (PNG only)

Returns the rendered image as base64-encoded data, so MCP clients can display it inline.

Example

Ask your LLM:

"Draw me a flowchart of the OAuth login flow"

It generates the Mermaid syntax, calls render_diagram, and you get back a PNG.

How it works

The server shells out to @mermaid-js/mermaid-cli (bundled as a dependency), which uses a headless Chromium to render diagrams. First npm install downloads Chromium (~150 MB), so it takes a few minutes.

Requirements

• Node.js 18+

Roadmap

• PDF export (formal/legal document workflows)
• draw.io XML export (editable diagrams)
• npm package (mermaid-render-mcp)
• Remote-hosted server option

License

MIT