d2-mcp.md

D2 MCP App

MCP App · UI in chat

from"h0rv"

h0rv maintains this Go MCP server for validating and rendering D2 diagrams. Release 2.0.0 bundles D2 0.9.0 and publishes an optional ui://d2/viewer resource that previews rendered diagrams with pan, zoom, fit, source copy and supported PNG downloads.

Not for: A visual diagram editor or document store. The viewer is read-only, the --ui flag is off by default, and the shipped server keeps no persistent diagram state.

Source and setup verified on 2026-11-05

Visualization

D2diagramsSVGviewer

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Quick facts

Maintainer: h0rv (community)
Release: d2-mcp 2.0.0 with D2 0.9.0
Transports: stdio, Streamable HTTP, legacy SSE
UI evidence: ui://d2/viewer; text/html;profile=mcp-app
UI switch: --ui; disabled by default

What you can do

Validate D2 syntax and return located diagnostics
Render diagrams as PNG, SVG or ASCII
Use bundled Dagre, ELK or open-source TALA layouts
Preview output with pan, zoom, fit and D2 source copy
Optionally read approved local .d2 files and write artifacts

Requirements

A d2-mcp 2.0.0 release binary, or Go 1.27.2+ to build it
An MCP Apps-compatible host for the inline viewer
The --ui flag when starting the server

setup.md

# 1. Download a release binary

Choose the 2.0.0 binary for Linux, macOS or Windows and verify it against the published SHA256SUMS file.

# 2. Make the binary executable

On Linux or macOS run chmod +x, then place the binary on PATH or keep its absolute path.

# 3. Enable the viewer

Add --ui to the stdio or HTTP command. Without that flag, the same diagram tools work but no app resource is advertised.

# Claude Desktop or another JSON-configured client → MCP client config

{
  "mcpServers": {
    "d2": {
      "command": "/absolute/path/d2-mcp",
      "args": ["--transport", "stdio", "--ui"]
    }
  }
}

Always confirm the latest setup instructions with the maintainer before installing.

>Questions

Does d2-mcp include a real MCP App viewer?

Yes. With --ui it serves ui://d2/viewer as text/html;profile=mcp-app and links compatible diagram tools to that resource.

Do I need the separate D2 executable?

No. The 2.0.0 release binaries bundle D2, the supported layout engines and native PNG rendering.

Can I edit a diagram directly in the viewer?

No. The viewer previews tool output and lets you copy source; ask the agent to change the D2 source and render again.

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