@arach/arc-mcp

MCP server for architecture diagrams as code.

Gives AI agents the full Arc toolchain over the Model Context Protocol — author, validate, lay out, render, and diff architecture diagrams from any MCP client.

Run it

No install needed — the server runs over stdio:

npx -y @arach/arc-mcp
# or: bunx @arach/arc-mcp

Client setup

Claude Code:

claude mcp add --scope project arc -- npx -y @arach/arc-mcp

Devin:

devin mcp add arc -- npx -y @arach/arc-mcp

Any MCP client (JSON config):

{
  "mcpServers": {
    "arc": {
      "command": "npx",
      "args": ["-y", "@arach/arc-mcp"]
    }
  }
}

Tools

| Tool | What it does | |------|--------------| | validate_diagram | Coded diagnostics for ArcDiagramData — consume by code, apply a supportedFixes entry, re-validate | | auto_layout | Auto-layout a full diagram or minimal input (nodeData + connectors + connectorStyles) | | diff_diagram | Structural DiagramDelta — feed to <ArcDiagram data={head} delta={delta} /> for a diff render | | render_svg | Deterministic SVG export — eleven themes, light/dark | | render_png | PNG raster via a local Chrome/Chromium binary (ARC_CHROME to override, ARC_CHROME=none to disable) | | render_html | React component snippet, iframe embed, or standalone HTML page | | render_ascii | Unicode/ASCII box-art rendering for terminals and docs | | diagram_to_typescript | Emit a typed ArcDiagramData TypeScript module | | editor_handoff | Build URLs that open the diagram in the Arc studio |

Resources

| URI | Content | |-----|---------| | arc://schema/diagram | Generated draft-07 JSON Schema for ArcDiagramData | | arc://skill/diagrams | Arc diagram-generation skill for agents | | arc://docs/llm | Dense LLM briefing |

Self-hosting over HTTP

The published bin runs over stdio, which is all a local client needs. To serve Arc to clients on other machines, run the Streamable HTTP server from a checkout of the repo:

git clone https://github.com/arach/arc && cd arc
bun install
ARC_MCP_HOST=127.0.0.1 ARC_MCP_PORT=5190 bun run mcp:http
# MCP endpoint: http://127.0.0.1:5190/mcp · health: /health

| Variable | Default | Purpose | |----------|---------|---------| | ARC_MCP_PORT | 5190 | Port to listen on | | ARC_MCP_HOST | 0.0.0.0 | Interface to bind; use 127.0.0.1 unless it sits behind your own auth | | ARC_EDITOR_URL | http://localhost:5188 | Studio base that editor_handoff links point to |

Arc doesn't run a public MCP endpoint. If you need a hosted one, open an issue at github.com/arach/arc.

Related packages

• @arach/arc — React renderer, visual studio, arc CLI, ASCII renderer
• @arach/arc-viewer — native Mermaid sequence diagrams + Mermaid import
• @arach/arc-iso — isometric renderer for vanilla JS and the browser

Studio + docs: arc.jdi.sh · Source: github.com/arach/arc

License

MIT