Mermaid Validator MCP server

This MCP server validates and renders Mermaid diagrams, making it easier for Large Language Models to create and verify diagram syntax. It ensures your diagrams are syntactically correct and provides rendered PNG output for visual confirmation.

Installation

You can configure your MCP client to use the Mermaid Validator by adding it to your MCP servers configuration file:

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

Usage

Validating Mermaid Diagrams

The server provides a validateMermaid tool that accepts Mermaid diagram syntax as input. When you submit a diagram, the server will:

1. Check if the syntax is valid
2. Render the diagram as a PNG if valid
3. Return validation results and the rendered image

Example Responses

Successful Validation

When your diagram is valid, you'll receive:

• A confirmation text message stating "Mermaid diagram is valid"
• A base64-encoded PNG image of your rendered diagram

Failed Validation

If your diagram contains syntax errors, you'll receive:

• A message stating "Mermaid diagram is invalid"
• An error message explaining what went wrong
• Detailed error output (when available) to help you fix the issue

Integration with MCP Clients

This server works with any MCP-compatible client. After adding the configuration to your MCP servers file, your client should automatically detect and use the Mermaid validation tool when needed.

Technical Details

API Specification

The server exposes the validateMermaid tool with the following parameters:

• diagram (string): The Mermaid diagram syntax to validate

The tool returns content that includes validation status text and, if valid, the rendered PNG image.

How to install this MCP server

For Claude Code

To add this MCP server to Claude Code, run this command in your terminal:

claude mcp add-json "mermaid-validator" '{"command":"npx","args":["-y","@rtuin/mcp-mermaid-validator@latest"]}'

See the official Claude Code MCP documentation for more details.

For Cursor

There are two ways to add an MCP server to Cursor. The most common way is to add the server globally in the ~/.cursor/mcp.json file so that it is available in all of your projects.

If you only need the server in a single project, you can add it to the project instead by creating or adding it to the .cursor/mcp.json file.

Adding an MCP server to Cursor globally

To add a global MCP server go to Cursor Settings > Tools & Integrations and click "New MCP Server".

When you click that button the ~/.cursor/mcp.json file will be opened and you can add your server like this:

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

Adding an MCP server to a project

To add an MCP server to a project you can create a new .cursor/mcp.json file or add it to the existing one. This will look exactly the same as the global MCP server example above.

How to use the MCP server

Once the server is installed, you might need to head back to Settings > MCP and click the refresh button.

The Cursor agent will then be able to see the available tools the added MCP server has available and will call them when it needs to.

You can also explicitly ask the agent to use the tool by mentioning the tool name and describing what the function does.

For Claude Desktop

To add this MCP server to Claude Desktop:

1. Find your configuration file:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json
• Linux: ~/.config/Claude/claude_desktop_config.json

2. Add this to your configuration file:

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

3. Restart Claude Desktop for the changes to take effect