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Mermaid Validator

v1.0.0•Developer Tools•stable

A Model Context Protocol server that validates and renders Mermaid diagrams.

mcpmermaidmodel-context-protocol
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What is Mermaid Validator?

Mermaid Validator is a Model Context Protocol (MCP) server that allows AI assistants like Claude, Cursor, and VS Code to model context protocol server that validates and renders mermaid diagrams.

A Model Context Protocol server that validates and renders Mermaid diagrams.

This server falls under the Developer Tools category on MCPgee, the world's largest MCP server directory with 33,000+ servers.

Features

  • validateMermaid

Use Cases

Mermaid diagram validation
Diagram rendering and code quality
rtuin

Maintainer

LicenseMIT License
Languagejavascript
Versionv1.0.0
UpdatedApr 3, 2026
Statushealthy
Maintenanceactive

Works with

ClaudeOpenAIwindowsmacoslinux
View SourceBrowse All Servers

Installation

NPM

npx -y @rtuin/mcp-mermaid-validator

Manual Installation

npx -y @rtuin/mcp-mermaid-validator

Configuration

Configuration Details

Config File

claude_desktop_config.json

Performance

Response Metrics

Response Time< 200ms
ThroughputMedium

Resource Usage

Memory UsageLow
CPU UsageLow

How to Set Up and Use Mermaid Validator

MCP Mermaid Validator is a Model Context Protocol server that validates Mermaid diagram syntax and renders valid diagrams to PNG images, returning them as base64-encoded content that MCP clients can display inline. Built on the official Mermaid CLI, it exposes a single validateMermaid tool that catches syntax errors with descriptive messages and confirms correctness with a rendered image. Developers use it to let AI assistants verify generated diagram code in real time before inserting it into documentation, pull requests, or design documents.

Prerequisites

  • Node.js 18+ with npx available
  • An MCP-compatible client that supports image content (e.g. Claude Desktop)
  • No additional API keys or accounts required
1

Test the server directly with npx

No installation is required. npx downloads and runs the package on demand. Confirm it starts without errors.

npx -y @rtuin/mcp-mermaid-validator@latest
2

Add the server to your MCP client configuration

Insert the mermaid-validator entry into claude_desktop_config.json. The server runs entirely locally with no external service calls.

{
  "mcpServers": {
    "mermaid-validator": {
      "command": "npx",
      "args": [
        "-y",
        "@rtuin/mcp-mermaid-validator@latest"
      ]
    }
  }
}
3

Restart your MCP client

Restart Claude Desktop (or your chosen MCP client) so it discovers the mermaid-validator server and loads the validateMermaid tool.

4

Verify the tool is available

Ask Claude to list available tools or simply try validating a simple diagram. A valid diagram will return a PNG preview; an invalid one will return an error message with details.

Mermaid Validator Examples

Client configuration

Claude Desktop config to run the Mermaid Validator via npx with no environment variables required.

{
  "mcpServers": {
    "mermaid-validator": {
      "command": "npx",
      "args": [
        "-y",
        "@rtuin/mcp-mermaid-validator@latest"
      ]
    }
  }
}

Prompts to try

Sample prompts that exercise the validateMermaid tool.

- "Validate this Mermaid diagram and show me the rendered image:\ngraph TD\n  A[Start] --> B{Decision}\n  B -->|Yes| C[Action]\n  B -->|No| D[End]"
- "Generate a sequence diagram showing a user login flow and validate it."
- "Check if this Mermaid syntax is correct: flowchart LR\n  id1((Circle)) --> id2[Rectangle]"
- "Create a class diagram for a simple e-commerce system and render it."
- "I wrote this Mermaid chart but it's not working — can you find the syntax error and fix it?"

Troubleshooting Mermaid Validator

npx fails with 'ENOENT' or 'package not found'

Ensure you are using Node.js 18+ (node --version) and that npx is available. Run 'npm install -g npm@latest' to update npm if the package registry lookup fails.

Rendered PNG is not displayed in the MCP client

Not all MCP clients render image content returned by tools. Claude Desktop supports inline images; Cursor may not display SVG but the server uses PNG by design for broader compatibility. Check your client's documentation for image content support.

Validation returns errors for valid-looking Mermaid syntax

Mermaid syntax is version-sensitive. The validator uses the version of @mermaid-js/mermaid-cli bundled with the package. Ensure your diagram uses syntax compatible with the installed CLI version. Check the output error text for the specific token or line causing the failure.

Frequently Asked Questions about Mermaid Validator

What is Mermaid Validator?

Mermaid Validator is a Model Context Protocol (MCP) server that model context protocol server that validates and renders mermaid diagrams. It connects AI assistants to external tools and data sources through a standardized interface.

How do I install Mermaid Validator?

Install via npm with the command: npx -y @rtuin/mcp-mermaid-validator. Then add the server configuration to your AI client's JSON config file (e.g., claude_desktop_config.json or .cursor/mcp.json).

Which AI clients work with Mermaid Validator?

Mermaid Validator works with all major MCP-compatible AI clients including Claude Desktop, Claude Code, Cursor, VS Code (GitHub Copilot), Windsurf, and Cline.

Is Mermaid Validator free to use?

Yes, Mermaid Validator is open source and available under the MIT License license. You can use it freely in both personal and commercial projects.

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Quick Config Preview

{ "mcpServers": { "mcp-mermaid-validator": { "command": "npx", "args": ["-y", "@rtuin/mcp-mermaid-validator"] } } }

Add this to your claude_desktop_config.json or .cursor/mcp.json

Read the full setup guide →

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