archlang-mcp

@chanmeng666/archlang-mcp

A Model Context Protocol server for ArchLang — author, inspect, and repair architectural floor plans written as code, from any MCP-speaking host.

It is a thin stdio shim over the @chanmeng666/archlang library (no subprocess, no re-implementation): each tool wraps one pure, exported function. The core stays zero-dependency — the MCP SDK lives only in this package.

When to prefer the CLI

ArchLang's primary agent interface is the agent-native archlang CLI, not this server. A CLI costs nothing in an agent's context window until it is called, whereas an MCP tool schema sits in the window permanently. If your agent already has a shell, prefer:

npx -y @chanmeng666/archlang context     # the whole language + workflow + CLI + errors, one call
npx -y @chanmeng666/archlang compile plan.arch -o out.svg --json

After npm i -g @chanmeng666/archlang the same calls are archlang context and archlang compile …. The package also installs an arch alias, but on Linux, macOS and Git Bash coreutils ships its own arch, so a bare arch there runs the wrong program.

This MCP server exists so MCP-native hosts can discover ArchLang through the registry and drive it without a shell. It is listed on the official MCP registry as io.github.ChanMeng666/archlang-mcp. It is the discoverability channel, not a replacement. See ADR 0012 (which amends ADR 0009's distribution-over-protocol stance).

Server instructions

At initialize the server sends a short instructions string, which hosts that support it add to the model's context: read the archlang://spec resource first, then write .arch → compile (and fix) → describe → validate with strict:true → finish before export. It is SKILL.md's loop, condensed, and a test holds the commands it names to the CLI manifest and to that loop's order.

Tools

Every tool takes ArchLang source (a plan "…" { … } string) and returns structured JSON. compile also accepts plan_json (the Plan-JSON / RPLAN shape).

Tool	What it does
compile	Render source (or plan_json) to SVG, or to zero-dep ASCII (format:"txt"), Plan JSON as an object (format:"json", the shape plan_json takes) or a PNG image (format:"png", at archlang preview's width unless width overrides it, within a clamped range; needs the optional @resvg/resvg-js, which the .mcpb bundle leaves out). accessible, overlay:"circulation" opt-ins. Returns output + diagnostics. A multi-storey plan returns every storey in pages[]; level renders one.
describe	Semantic facts (rooms, areas, adjacency, doors, circulation, zones, storeys, the exact floor_polygon/floor_circle shape, and a freedom report of which positions are hand-authored vs resolver-derived) — verify intent without an image.
lint	Advisory W_* soundness warnings (may include the fix-carrying W_ALIAS_MATCH for a room use inferred from an indirect label alias); profile selects a ruleset.
validate	Parse + resolve + lint, the ship gate. strict fails on warnings; graph checks interior-door adjacency against an intended room graph; intent gates on a brief's contract (per archlang://intent-schema).
score	The continuous intent METER: how much of a brief a plan satisfies (satisfied/total/score/subscores). Measures, never gates.
repair	Explicit corrector: furniture out of walls/doorways/swings → new .arch source + change log. Never adds doors/windows.
finish	Complete the drawing: furnish the rooms that hold no furniture, then add the missing paper, scale, dims auto, title, schedule rooms and legend → new .arch source + change log. Fills only what is missing; only runs one stage (furnish or sheet); reissue may replace paper/scale.
fix	Apply the machine-applicable fixes on a plan's diagnostics (syntactic corrector; bounded fixpoint). unsafe widens to maybe-incorrect.
suggest	Advisory door/window statements (each referencing its wall by a stable ref — an authored id or a unique category — or absolute coordinates, never a re-bindable positional id) to resolve unreachable rooms / windowless bedrooms — data, never applied.
complete	LSP completion items in scope at a source byte offset.
link	Two URLs that show the plan in a browser with nothing to install: playground (the hosted editor, rendered) and embed (the plan alone, for an iframe), plus bytes, the compressed plan's size, and ok (with an errors count when the plan does not compile; it still links and the page shows the diagnostics). The plan rides in the URL fragment. Needs a core that exports ./link; an older one gets ok:false and the version it needs.

What compile's accessible does here — and what it does not

accessible: true gives the SVG its <title>/<desc> pair and role="img" on the root, which is the whole of the option as this shim exposes it. The v1.36 element controls are not reachable through MCP. They need annotate alongside accessible, and this tool passes annotate only for format:"txt"; it also takes accessible as a boolean, so the { idPrefix } form that keeps several plans on one HTML page from sharing arch-title/arch-desc cannot be requested either.

A host that needs a keyboard- and screen-reader-operable drawing — data-arch-primary, role="button", aria-label on each element — has to call the library. The CLI cannot produce it either: annotate has no flag, so archlang compile --accessible stops at the <title>/<desc> pair too.

import { compile } from "@chanmeng666/archlang";
compile(src, { annotate: true, accessible: { idPrefix: "plan-7" } });

The output contract, what an embedder still owns, and the known screen-reader limitations are in the language reference.

Resources

URI	Content
archlang://spec	The whole language in one page (spec.llm.md).
archlang://context	Full agent context: spec + workflow + CLI reference + error catalog (llms-full.txt).
archlang://schema	JSON Schema (2020-12) for the Plan-JSON compile input.
archlang://grammar	GBNF constrained-decoding grammar for guaranteed-parseable generation.
archlang://intent-schema	JSON Schema (2020-12) for a brief's Intent — the shape validate's intent and score's brief take.

Install

Claude Code

claude mcp add archlang -- npx -y @chanmeng666/archlang-mcp

Claude Desktop

Add to claude_desktop_config.json (Settings → Developer → Edit Config):

{
  "mcpServers": {
    "archlang": {
      "command": "npx",
      "args": ["-y", "@chanmeng666/archlang-mcp"]
    }
  }
}

Cursor

Add to .cursor/mcp.json (project) or ~/.cursor/mcp.json (global):

{
  "mcpServers": {
    "archlang": {
      "command": "npx",
      "args": ["-y", "@chanmeng666/archlang-mcp"]
    }
  }
}

VS Code

Add to .vscode/mcp.json:

{
  "servers": {
    "archlang": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@chanmeng666/archlang-mcp"]
    }
  }
}

License

MIT © Chan Meng