Use ArchLang from an AI agent

ArchLang is built to be driven by an AI agent end-to-end — through its CLI, with no server and nothing to configure. An agent can learn the whole language, author a plan, render it, and verify it matches intent without ever looking at an image — token-cheap and in any harness.

No install

• In ChatGPT: ArchLang app in ChatGPT.
• In claude.ai: add https://mcp.archlang.uk/mcp as a custom connector.

CLI first — but there is an MCP server too. A CLI costs nothing in an agent's context until it is called; an MCP server's tool schemas sit in the context window permanently. So the CLI (plus a filesystem Skill) stays the primary interface, and an agent with a shell should use it. But an MCP-native host that cannot run a shell command needs a way to reach ArchLang at all, so an optional stdio shim — @chanmeng666/archlang-mcp, listed on the MCP registry — wraps the same pure library functions. It is a discoverability channel, not a replacement; the core stays zero-dependency. A hosted copy answers at https://mcp.archlang.uk/mcp. Setup for each host is on the MCP server page; the reasoning is ADR 0012.

Install into your coding agent

npx skills add ChanMeng666/archlang                      # the ArchLang skills, for any agent that reads skills
claude mcp add archlang -- npx -y @chanmeng666/archlang-mcp   # or the MCP server (Claude Code shown)
/plugin marketplace add ChanMeng666/archlang                # or, inside Claude Code: the skill + MCP server as one plugin
/plugin install archlang@archlang

npx skills add ChanMeng666/archlang offers five skills (add --yes to install them all without asking). Start from archlang, the full workflow; the other four are task skills, short checklists for one job each. The Claude Code plugin loads all five.

• archlang-brief-to-plan: write a new plan from a written brief and check it against the brief.
• archlang-edit-plan: change an existing .arch with the smallest edit, then re-verify.
• archlang-export: deliver SVG, PNG, PDF or DXF files, with paper size, scale and storeys.
• archlang-review-plan: check a plan (lint profiles, the intent gate, suggestions) without editing it.

To see what agents produce from a one-paragraph brief, open the agent gallery.

Then ask in plain language; the agent writes the .arch, compiles it, and checks it with lint and describe:

• "Design a one-bedroom flat of about 54 m²: a 32 m² living/kitchen, a 10 m² bedroom and a 10 m² bathroom, with the front door on the north wall."
• "Draw a two-storey, two-bedroom house, 8 m × 6 m, with a stair linking the floors, and give me one SVG per storey."
• "Export that plan as DXF."

Zero-install

npx -y @chanmeng666/archlang help

The recommended forms are npx -y @chanmeng666/archlang <cmd>, or npm i -g @chanmeng666/archlang followed by archlang <cmd>; this page writes the short one. Two names look shorter and are wrong: the unscoped npm package archlang belongs to someone else, and a bare arch runs the coreutils command on Linux, macOS and Git Bash. (The package installs arch as an alias too.)

Cold start

One call gives a fresh agent everything — the language spec, the authoring workflow, the CLI reference and the error catalog, as a single system-prompt-ready bundle:

archlang context          # == llms-full.txt

Take one slice of it when that is all you need: archlang context --section errors prints just the diagnostic catalog: the catalog alone is about 67 KB, where the bundle is about 160 KB in all. The sections are spec (the language), workflow (the agent loop), cli (every command) and errors. If you only need the language, archlang spec prints the one-page spec.

Discovery

Ask the CLI, don't guess at it. archlang help lists every command; archlang <cmd> --help (or archlang help <cmd>) prints that one command's flags and worked examples — cheaper than pulling the whole manifest into your context. archlang --version prints the version, and archlang manifest --json still serves the entire CLI as data when you'd rather parse than read. Help and the reference are both rendered from that one manifest, so neither can drift from the tool.

The loop

1. Learn the language — archlang spec (or archlang context for spec + workflow + CLI + errors).
2. Write a .arch file (or pipe source via stdin with -).
3. Render — archlang compile plan.arch -o plan.svg --json. The JSON is { ok, diagnostics, summary }.
4. Self-correct — if ok is false (exit code 2), read each diagnostics[].fix (with line/col). Many diagnostics also carry machine-applicable fixes: archlang fix plan.arch applies them, rewriting the file in place (--backup keeps the original as plan.arch.bak; -o out.arch writes elsewhere), and archlang fix plan.arch --dry-run --json previews them without touching disk. Either way fix prints the unified diff it would write to stderr, so you see the edit before you trust it — and the mechanical edits don't cost you a turn.
5. Verify intent without an image — archlang describe plan.arch --json returns rooms (uses, areas, adjacency), what each door/window/opening connects, the furniture, an access graph (entrances, per-room reachability and depth), and totals. Confirm the room count, labels, and areas match the brief. On a big plan, read only what you're checking: --select rooms,totals keeps just those top-level keys, and --room kitchen,bath keeps just those rooms plus the doors/windows/furniture touching them. archlang compile -f txt will even print a zero-dependency ASCII plan if you want to "look" without a raster.
6. Check soundness — archlang lint plan.arch --json flags habitability problems (a room with no door, a windowless bedroom, an implausibly small room, a too-narrow door, no entrance, a fixture floating off the wall). Tighten the bar with --profile accessibility-advisory, or narrow the read with --code W_ROOM_UNREACHABLE / --severity error (both also on validate). For the faults lint can't fix on its own (an unreachable room, a windowless bedroom), archlang suggest --json returns the door/window statements that would resolve them — as data, for you to choose from.
7. Gate on the brief — write the brief down as an intent contract and archlang validate plan.arch --intent brief.json --feedback --json fails (exit 2) when the plan misses a gating expectation. archlang score --brief brief.json --json gives the continuous satisfied/total reading instead — it measures, it never gates.
8. Finish the drawing — once lint is clean, archlang finish plan.arch --dry-run --json lists the furniture and sheet statements (paper, scale, dimensions, title, room schedule, legend) it would add, and archlang finish plan.arch adds them. Read unresolved: every room it left empty and every statement it left out is named there with the reason.
9. Show the user the result — archlang preview plan.arch -o plan.png renders a viewable PNG (~1600px, legible enough for your own vision and small enough to ingest). If it reports E_PNG_DEPENDENCY, re-run with --install. To give a person the plan itself, rendered and with nothing to install, npx -y @chanmeng666/archlang link plan.arch prints a playground URL that opens it.

A display filter never changes gating. --select, --room, --code and --severity narrow what you read; ok and the exit code are always computed from the unfiltered diagnostic set, and a narrowed result says so (filtered: true, total_diagnostics: n). Bounding your context can never hide a failure from you.

Every command and flag is on the CLI reference — generated from the same manifest archlang manifest --json serves, so it cannot fall behind the tool.

Exit codes & JSON

Every command takes --json (structured result on stdout, human messages on stderr) with deterministic exit codes: 0 ok · 2 user-source error (fix it, don't blindly retry) · 1 IO/internal · 3 bad usage. Every JSON diagnostic carries the catalogued fix — in human mode it prints as a = fix: line, so you never need a second call to archlang explain to know the remedy.

A mistyped flag or verb is a usage error (3), never a silently ignored argument: archlang lint plan.arch --jsn exits 3 with a did-you-mean (--json) and a usage: echo, and archlang comple suggests compile. Treat a 3 as "read the help" (archlang <cmd> --help), not "retry".

Example: describe as a verification channel

For the studio example, archlang describe --json returns (abridged):

{
  "ok": true,
  "plan": "Studio 1BR",
  "bbox": { "w": 7000, "h": 6000 },
  "rooms": [
    { "id": "r_living", "label": "Living / Kitchen", "uses": ["living", "kitchen"], "area_m2": 24, "net_area_m2": 22.33, "adjacent": ["r_bed", "r_hall", "r_bath"] },
    { "id": "r_bed", "label": "Bedroom", "uses": ["bedroom"], "area_m2": 9, "net_area_m2": 8.12, "adjacent": ["r_living", "r_hall"] }
  ],
  "doors": [ { "id": "d_bath", "between": ["r_hall", "r_bath"], "width": 800 } ],
  "openings": [ { "id": "o_living", "between": ["r_living", "r_hall"], "width": 900 } ],
  "access": {
    "entrances": ["d_main"], "hasEntrance": true,
    "rooms": [ { "id": "r_bath", "depthFromEntrance": 3, "reachable": true, "bottleneckClearWidth": 740 } ]
  },
  "totals": { "rooms": 4, "floor_area_m2": 42, "gross_internal_area_m2": 39.44, "net_floor_area_m2": 38.29 }
}

A text-only agent can read this and confirm "4 rooms, 42 m² on wall centrelines (39.44 m² inside the shell, 38.29 m² net of every wall), the bath reached off the hall (not through the bedroom), every room reachable from the front door" — no rendering required. See the full schema.

describe --json also reports freedom: for every placed element, whether its coordinates were hand-authored or derived by the resolver. Read it before nudging a number — it tells you which positions are yours to move and which fall out of the layout.

Machine-readable artifacts

Served at this site's root, so a tool can fetch them directly:

Every top-level docs page also serves its raw markdown at /<route>.md (e.g. /cli.md; the home page's copy is /index.md). The /adr/… pages have no raw copy.

Show a plan on a web page

A page can compile a plan in the reader's browser, with no server. Import compile from the core's pinned jsDelivr +esm URL and set the SVG yourself; that form works in a Claude Code artifact. Or load https://archlang.uk/arch-plan.js and write <arch-plan src="https://archlang.uk/examples/studio.arch"></arch-plan>. Both are on Embed a floor plan in a web page.

Also

• The same functions are exported from the library — compile, describe, lint, validateIntent, taste, repair, applyFixes, suggestTopology, renderAscii and more: import { compile, describe, lint } from "@chanmeng666/archlang". See the JavaScript library.
• These power the live preview, Describe, Lint and Intent tabs in the playground.
• See SKILL.md and llms.txt in the repo.