README.md
An MCP server that validates Mermaid diagram syntax.
Mermaid Validator MCP
A Model Context Protocol (MCP) server built with Bun and TypeScript that validates Mermaid diagram syntax.
Quick Start
This package is published on npm. You can run it directly with npx:
npx -y mermaid-validator-mcp
MCP Client Configuration
Add the server to your MCP client (e.g. Claude Desktop) configuration:
Using npx (recommended)
{
"mcpServers": {
"mermaid-validator": {
"command": "npx",
"args": ["-y", "mermaid-validator-mcp"]
}
}
}
Using local source
{
"mcpServers": {
"mermaid-validator": {
"command": "bun",
"args": [
"/path/to/mermaid-validator-mcp/index.ts"
]
}
}
}
Or if you have it installed globally:
{
"mcpServers": {
"mermaid-validator": {
"command": "mermaid-validator-mcp"
}
}
}
Features
- Single tool –
validate_mermaid: Pass any Mermaid diagram text and receive either a success response with the detected diagram type, or a detailed parse-error message. - Supports all major Mermaid diagram types: flowchart, sequence, class, pie, gantt, state, ER, gitGraph, mindmap, timeline, and more.
- No dependency on
mermaid-clior any external rendering process. - Uses JSDOM to provide the minimal DOM environment required by Mermaid.
Requirements
- Bun ≥ 1.0
Getting Started
# Install dependencies
bun install
# Start the MCP server (stdio mode)
bun start
Tool: `validate_mermaid`
Input
| Field | Type | Description |
|---|---|---|
diagram |
string | The Mermaid diagram text to validate |
Output (JSON text)
Valid diagram
{ "valid": true, "diagramType": "flowchart-v2" }
Invalid diagram
{
"valid": false,
"error": "Parse error on line 2:\n...TD\n --> B\n-------^\nExpecting 'SEMI', ..."
}
Development
# Run with auto-reload
bun dev
# Build
bun run build
Tools (1)
validate_mermaidValidates Mermaid diagram text and returns the diagram type or a detailed parse-error message.Configuration
claude_desktop_config.json
{"mcpServers": {"mermaid-validator": {"command": "npx", "args": ["-y", "mermaid-validator-mcp"]}}}Try it
→Validate this Mermaid flowchart syntax: graph TD; A-->B;
→Check if this sequence diagram is valid: sequenceDiagram; Alice->>John: Hello John, how are you?
→Can you validate this ER diagram code for me?
→Identify the diagram type and check for syntax errors in this Mermaid string.