ArchLang

ArchLang vs Mermaid for floor plans ​

ArchLang is an open-source language for floor plans, created by Chan Meng: you write .arch text and compile it to SVG, DXF or PDF.

Mermaid has no floor-plan diagram type. Its diagrams — flowcharts, sequence, class, state, ER, Gantt, architecture and others — lay out boxes and arrows automatically, and none of them draws walls, doors and windows at a real size. A floor-plan syntax for Mermaid has been requested in mermaid-js/mermaid#6134 ("Add Floorplan Syntax"), which is open as of November 2026.

ArchLang is not part of Mermaid and is not a Mermaid plugin. It is a separate text language with the same idea — a diagram you write as text and keep next to your code — applied to floor plans.

The same plan, in each ​

A kitchen open to a dining room, with one front door. In Mermaid the nearest you can get is a graph of which room connects to which:

mermaid
flowchart LR
  Entrance --> Dining
  Dining --- Kitchen

That records the connections, but no size, position, wall or window. In ArchLang the plan carries all of them, in millimetres. Edit it below and it recompiles:

arch
plan "Kitchen and dining" {
  units mm
  grid 50
  room id=kitchen at (0,0)          size 3000x3600 label "Kitchen" uses kitchen
  room id=dining  right-of kitchen  size 4000x3600 label "Dining" uses dining
  walls from rooms exterior 200 partition 100 {
    open between kitchen and dining width 1800
  }
  door on dining.bottom at center width 900 swing into dining
  window on kitchen.top width 1200
  window on dining.top width 1800
  furniture kitchen_sink against kitchen.top
  furniture stove against kitchen.left
  furniture counter against kitchen.left offset 2600
  furniture dining_table in dining centered size 1600x900
}

npx -y @chanmeng666/archlang describe on this source reports a 10.8 m² kitchen and a 14.4 m² dining room, and that the kitchen is reached from the front door through the dining room — the same connection the Mermaid graph states, here derived from the drawing.

Side by side ​

MermaidArchLang
What it drawsFlowcharts, sequence, class, state, ER, Gantt and other diagramsFloor plans: walls, rooms, doors, windows, furniture, dimensions, stairs
LayoutAutomaticExact: coordinates and sizes in millimetres, or rooms placed relative to each other
MeasurementsNoneRoom areas, door widths, walking distances, reported by describe
ChecksSyntaxSyntax, plus advisory warnings such as a windowless bedroom or a narrow door (lint)
OutputSVG; PNG and PDF through mermaid-cliSVG, DXF, PDF, PNG, ASCII
Renders in GitHub MarkdownYes, nativelyNo; render fences to images with archlang md or the arch-render GitHub Action
LicenceMITMIT

When to use which ​

Use Mermaid for the diagrams it has: process flows, sequences, data models, timelines. It is built into GitHub, GitLab and many documentation tools, so a fence renders with nothing to install.

Use ArchLang when the diagram is a floor plan: when sizes, areas or door positions matter, when the plan should open in CAD (DXF), or when an AI model writes the plan and needs to check it. A bubble diagram of which rooms connect is fine in Mermaid; once it needs walls, it is a floor plan.

Floor plans in Markdown ​

GitHub does not render arch fences. Two ways to put the drawing in a Markdown file:

bash
npx -y @chanmeng666/archlang md notes.md -o notes.out.md -f svg   # each arch fence becomes an image link

The md command writes notes.out.md with every arch fence replaced by an image link, and the SVG files beside it. In CI, the ChanMeng666/archlang/.github/actions/arch-render GitHub Action does the same for every Markdown file in a repository. In VS Code, the ArchLang extension renders arch fences in the built-in Markdown preview, and on this site every arch fence is a live, editable drawing.

FAQ ​

Can Mermaid draw floor plans? ​

No. Mermaid has no floor-plan diagram type; a request for one, mermaid-js/mermaid#6134, is open. A flowchart can show which rooms connect, but not their sizes, walls or openings.

Is there a Mermaid-like language for floor plans? ​

ArchLang is a text language for floor plans that you write in a fenced code block, like Mermaid. It compiles to SVG, DXF or PDF, and it is a separate project from Mermaid.

Can I render ArchLang in GitHub Markdown? ​

Not natively. Convert the fences to images with npx -y @chanmeng666/archlang md, or with the arch-render GitHub Action in CI, and commit the result.

Can I use Mermaid and ArchLang in the same document? ​

Yes. They use different fence languages (mermaid and arch), and the md command and the arch-render Action touch the arch fences and leave the rest of the file as it is.

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