About Arc
Arc is an MCP server for creating architecture diagrams as code. It gives AI agents tools to validate, lay out, render, and compare diagrams, with multiple export formats, themes, and related resources; it runs over stdio or a self-run HTTP service.
Key features
- 01Validate diagrams and return diagnostics
- 02Automatically lay out diagrams
- 03Render SVG, PNG, and animations
- 04Export HTML, ASCII, and TypeScript
- 05Produce structural diagram diffs
Use cases
- 01Generate architecture diagrams from coded data
- 02Check diagrams and apply supported fixes
- 03Export diagrams for documents or terminals
- 04Compare the structures of two diagram versions
MCP support
Arc exposes diagram validation, layout, rendering, and diff tools to MCP clients, along with schema, skill, and documentation resources. The published package runs over stdio; a Streamable HTTP service can also be started from a repository checkout.
Configuration
Local server config is the same for every client. Copy it into your client’s MCP config file.
Tools
10Saved tool list · updated 3d ago
| Parameter | Type | Required | Description |
|---|---|---|---|
| diagram | object | Yes | Arc diagram JSON object or JSON string |
| severity | enum | No | Filter returned diagnostics by severity (default: all)error | warning | all |
Details
From the project README
@hudsonkit/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 @hudsonkit/arc-mcp
# or: bunx @hudsonkit/arc-mcp
Client setup
Requires Node.js 22 or newer. No account, API key, or environment configuration is required. PNG export needs a local Chrome/Chromium installation; animation export also needs ffmpeg.
Claude Code:
claude mcp add --scope project arc -- npx -y @hudsonkit/arc-mcp
Devin:
devin mcp add arc -- npx -y @hudsonkit/arc-mcp
Any MCP client (JSON config):
{
"mcpServers": {
"arc": {
"command": "npx",
"args": ["-y", "@hudsonkit/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; authored flows animate via SMIL or sample at flowTime |
render_png | PNG raster via a local Chrome/Chromium binary (ARC_CHROME to override, ARC_CHROME=none to disable), sampled at flowTime |
render_animation | GIF/MP4 flow animation to an output path via Chrome frames + ffmpeg (ARC_FFMPEG to override) |
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/hudsonkit/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/hudsonkit/arc.
MCP Registry
Arc's registry identity is io.github.hudsonkit/arc. The install metadata lives
in server.json, and the npm package declares the same
mcpName so the registry can verify ownership.
Maintainers can run the Publish to npm GitHub Actions workflow with package
scope mcp for an MCP-only patch release, or all for a coordinated release.
The workflow sets both versions before building, verifies the packed server,
publishes npm, then publishes the registry metadata using GitHub OIDC. A dry run
validates and packs without publishing. GitHub's curated MCP catalog requires
initial onboarding
after publication to the official MCP Registry.
Related packages
@hudsonkit/arc— React renderer, visual studio,arcCLI, ASCII renderer@hudsonkit/arc-viewer— native Mermaid sequence diagrams + Mermaid import@hudsonkit/arc-iso— isometric renderer for vanilla JS and the browser
Studio + docs: hudsonkit.com/arc · Source: github.com/hudsonkit/arc
License
Comments
New to MCP?
From what the protocol is to installing your first server, these answers cover most first questions.
An open protocol that defines how AI applications connect to external tools and data in a uniform way. Clients talk to the model; MCP servers provide tools, resources and prompt templates. They exchange standard messages, so one server can be reused by many clients.