MCP Mermaid

npx -y mcp-mermaid

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

Mermaid is the natural diagram format for a model because it is text, but the failure mode is silent: one malformed edge and the renderer produces nothing useful. This server validates the definition before rendering and reports the problem, which turns diagramming into a correction loop the model can finish on its own across a couple of turns. Output format is chosen per call — base64, raw SVG, the Mermaid source itself, a file written to disk for coding agents, or a shareable mermaid.ink URL — and background colour and theme are parameters, so styling does not require post-processing. It runs over stdio or as an SSE or streamable HTTP service, with a Docker image for the server mode.