drawio-mcp-server

An MCP (Model Context Protocol) server for draw.io / diagrams.net with an interactive, editable diagram UI.

It exposes tools to build a diagram from a structured description (nodes + edges) and render it on an embedded, editable draw.io canvas right inside the client — where the user can keep editing and export to PNG, SVG, or XML.

Modeled on googlemaps-mcp-server: same MCP-App pattern (data tools return content, a UI tool returns an embedded interactive HTML resource), but no authentication — draw.io is fully client-side, so there are no API keys and no OAuth.

Prerequisites

Node.js 18+
pnpm

Setup

Install:

pnpm install

Build and run:

pnpm dev

The server starts on port 3000 and exposes the MCP endpoint at /mcp.

Environment Variables

Variable	Required	Description
`PORT`	No	Port to listen on (default: `3000`)

Endpoints

Endpoint	Description
`/mcp`	MCP endpoint (GET, POST, DELETE) — no auth required
`/health`	Health check

MCP Tools

`create_diagram`

Build a draw.io diagram from a structured description and return valid mxGraph XML.

Parameters:

nodes (required) — array of { id, label?, shape?, x?, y?, width?, height?, fillColor?, strokeColor? }. shape is one of rectangle, rounded, ellipse, diamond, process, terminator, cylinder, cloud, hexagon, parallelogram.
edges — array of { source, target, label?, dashed? } referencing node ids.
direction — vertical (default) or horizontal, used by the auto-layout when positions are omitted.

Positions are auto-laid-out (layered, centered) when x/y are omitted — just describe what connects to what.

`render_diagram`

Display the diagram inline. Renders ready-made mxGraph xml (typically the output of create_diagram); omit xml to open a blank canvas. Building from a description lives in create_diagram, so this tool only renders.

Parameters: xml (the diagram to render — omit for a blank canvas), title (optional).

The diagram opens in the full draw.io editor (embed.diagrams.net in a nested iframe, JSON postMessage protocol) — shape palette, live editing, autosave — with PNG / SVG / XML export buttons and an "Edit in draw.io" button that opens the standalone web editor in a new tab with the diagram preloaded.

Fallback: if the editor embed never initializes (a host enforcing CSP frame-src 'none', network block, …) the UI swaps to the read-only draw.io viewer (viewer-static.min.js, an in-document script — no nested iframe) and shows a notice. The resource declares _meta.ui.csp.frameDomains for embed/app.diagrams.net so hosts that honor resource-declared CSP keep the editor working; hosts that apply no CSP to MCP-app sandboxes (Langdock today) render the editor as-is.

Resources

`ui://drawio/editor`

The diagram UI rendered by render_diagram, served as an MCP App resource: the embedded draw.io editor with a read-only viewer fallback.

Client Configuration

{
  "mcpServers": {
    "drawio": {
      "type": "streamable-http",
      "url": "http://localhost:3000/mcp"
    }
  }
}

For a deployed server, replace the URL with your public endpoint, e.g. https://your-app.up.railway.app/mcp.

Deployment

The server is stateless and keyless — deploy the built dist/ and run pnpm start behind any HTTPS host (Railway, Fly, etc.). The only configuration is the optional PORT.