Drawio

Draw.io Diagram Skill

Generate draw.io diagrams as native .drawio files. Author each diagram either as Mermaid (concise text that the draw.io desktop CLI converts and lays out for you) or as draw.io XML directly. Optionally auto-layout XML-authored diagrams with ELK, export to PNG/SVG/PDF with the diagram XML embedded (so the exported file stays editable in draw.io), or generate a browser URL that opens the diagram directly in the draw.io editor.

Authoring: Mermaid or XML?

The desktop CLI can convert Mermaid to a native .drawio file, so prefer Mermaid for the diagram types it handles well — its parser lays the diagram out automatically, which is far more reliable than hand-positioning cells in XML.

• Prefer Mermaid when the desktop CLI is available and the request is one of the standard types above — write terse Mermaid and let draw.io lay it out.
• Use XML for precise control, or as the universal fallback: XML needs no CLI at all, so it's the only option when the desktop app isn't installed (output a .drawio file or a url).
• For XML-authored diagrams you can ask the CLI to apply an ELK auto-layout (--layout) instead of computing coordinates yourself — the same layouts the draw.io editor's Arrange ▸ Layout menu applies, and the same engine the draw.io MCP app server uses. See ELK layout for XML.

If you're unsure whether the desktop CLI is present, detect it first (see Locating the CLI). No CLI → author as XML and deliver a .drawio file or a url.

The pipeline

Every diagram becomes a native .drawio file first, then is delivered in the requested output format. This keeps the delivery step identical whether you authored Mermaid or XML.

1. Author → .drawio
   • Mermaid: write the Mermaid to a .mmd file, then convert it with the CLI:

     drawio -x -f xml -o diagram.drawio diagram.mmd
     

     Delete the .mmd afterward — the .drawio is the artifact. draw.io's Mermaid parser has already laid the diagram out, so no --layout is needed.
   • XML: write the mxGraphModel XML to diagram.drawio (see XML format). Optionally apply an ELK layout (see ELK layout for XML).
2. Deliver (identical for both sources):
   • (no format) → keep diagram.drawio and open it.
   • png / svg / pdf → export from the .drawio with embedded XML, then delete the source .drawio:

     drawio -x -f png -e -b 10 -o diagram.drawio.png diagram.drawio
     

   • url → build a browser URL from the .drawio XML, open it, and keep the .drawio as a local copy (see Browser URL output).
3. Open the result — the exported file, the URL, or the .drawio. If the open command fails, print the absolute path (or URL) so the user can open it manually.

Always convert Mermaid to .drawio first, then export — do not export a .mmd straight to an image. Direct Mermaid → PNG export with -e is broken in current draw.io Desktop (the embedded-XML step crashes); the two-step path (convert, then export the .drawio) is reliable and produces an editable embed. See Troubleshooting.

If Mermaid was requested but no desktop CLI is available, fall back to authoring the same diagram directly as XML.

ELK layout for XML

XML-authored diagrams can be auto-positioned by the CLI's --layout pass — the same ELK layouts as the editor's Arrange ▸ Layout menu and the same engine the draw.io MCP app server uses. Generate the cells with approximate (or even 0,0) positions and let ELK place them; you only have to get the graph structure — nodes and edges — right.

Add --layout <name> to any CLI call that reads your XML. The simplest form lays out in place after you write the file (reading and overwriting the same path is supported):

drawio -x -f xml --layout verticalFlow -o diagram.drawio diagram.drawio

Or combine layout with export in a single call (works for XML input):

drawio -x -f png -e -b 10 --layout verticalFlow -o diagram.drawio.png diagram.drawio

Layout presets

Custom layout JSON

For finer control, pass a JSON array (starting with [) instead of a preset name — the same format as the editor's custom-layout dialog:

drawio -x -f xml --layout '[{"layout":"elkLayered","config":{"elk.direction":"RIGHT"}}]' -o diagram.drawio diagram.drawio

Each entry is {"layout": <algorithm>, "config": { … }}:

• Algorithms: elkLayered, elkTree, elkRadial, elkOrganic, elkStress, elkBox.
• config: keys starting with elk. are ELK options — e.g. elk.direction (UP / DOWN / LEFT / RIGHT), elk.spacing.nodeNode, elk.layered.spacing.nodeNodeBetweenLayers. The keys edgeStyle (e.g. orthogonal) and corners (e.g. rounded) control connector rendering.

Orthogonal edge routing

--layout libavoid routes the edges orthogonally around the shapes (the editor's Arrange ▸ Layout ▸ Orthogonal Routing) without moving any vertex — the complement of the node layouts above. Use it as an in-place pass on hand-positioned XML whose connectors cross shapes:

drawio -x -f xml --layout libavoid -o diagram.drawio diagram.drawio

Skip it after a flow/tree preset — those already route their edges.

When to use it: author the graph structure as XML without worrying about coordinates, then apply verticalFlow / horizontalFlow for flow-style diagrams or organic for networks. Mermaid-authored diagrams are already laid out — don't add --layout.

Mermaid syntax reference

When authoring Mermaid, fetch and follow the shared Mermaid reference (all supported diagram types plus flowchart styling — style, classDef, linkStyle):

shared/mermaid-reference.md

Match the language of the diagram labels to the user's language.

Choosing the output format

Check the user's request for a format preference. Examples:

• /drawio:drawio create a flowchart → Mermaid → flowchart.drawio
• /drawio:drawio png flowchart for login → Mermaid → login-flow.drawio.png
• /drawio:drawio svg: ER diagram → Mermaid → er-diagram.drawio.svg
• /drawio:drawio pdf AWS architecture overview → XML (needs AWS shapes) → architecture-overview.drawio.pdf
• /drawio:drawio url flowchart for user login → opens browser at app.diagrams.net with the diagram, keeps login-flow.drawio locally

If no format is mentioned, just produce the .drawio file and open it in draw.io. The user can always ask to export later.

Supported export formats

PNG, SVG, and PDF all support --embed-diagram — the exported file contains the full diagram XML, so opening it in draw.io recovers the editable diagram.

Browser URL output

When the user requests url format, generate a draw.io URL that opens the diagram directly in the browser editor at app.diagrams.net — no draw.io Desktop required to view it. (Mermaid-authored diagrams still need the desktop CLI to convert to .drawio first; if no CLI is available, author the diagram as XML and build the URL from that.)

How it works

1. The .drawio file is written to disk as usual (gives the user a persistent local copy they can re-edit)
2. The XML is compressed with Node.js's built-in zlib and base64-encoded
3. The result is embedded in a https://app.diagrams.net/#create=... URL
4. The URL is opened in the default browser

This uses only Node.js built-in modules (zlib, child_process) — no external dependencies.

URL generation

Run this node -e one-liner to read the .drawio file and print the URL (replace DIAGRAM.drawio with the actual filename):

URL=$(node -e '
const fs = require("fs");
const zlib = require("zlib");
const xml = fs.readFileSync(process.argv[1], "utf8");
const compressed = zlib.deflateRawSync(encodeURIComponent(xml)).toString("base64");
const payload = encodeURIComponent(JSON.stringify({ type: "xml", compressed: true, data: compressed }));
console.log("https://app.diagrams.net/?grid=0&pv=0&border=10&edit=_blank#create=" + payload);
' "DIAGRAM.drawio")

The URL format matches the MCP Tool Server. Node.js's zlib.deflateRawSync and pako.deflateRaw both implement RFC 1951 and produce identical output, so URLs from either source are interchangeable.

Opening the URL

Why the .url workaround on Windows/WSL2? cmd.exe's start command treats & as a command separator and strips everything after # in URLs. The diagram payload lives in the #create=... fragment, so passing the URL directly causes it to be silently lost. A .url shortcut file preserves the URL intact.

macOS / Linux example:

open "$URL"      # macOS
xdg-open "$URL"  # Linux

WSL2 example:

TMPFILE=$(mktemp --suffix=.url)
printf '[InternetShortcut]\r\nURL=%s\r\n' "$URL" > "$TMPFILE"
cmd.exe /c start "" "$(wslpath -w "$TMPFILE")"

Windows (native) example:

Do not build the .url file with echo URL=%URL%. The generated URL contains & characters (?grid=0&pv=0&...) that cmd.exe treats as command separators, so the shortcut is written truncated and the diagram payload is lost — the exact failure the .url file is meant to prevent. Let Node write the file directly (it already holds the URL string) and open only the resulting path, which never contains &:

TMPFILE=$(node -e '
const fs = require("fs");
const os = require("os");
const path = require("path");
const p = path.join(os.tmpdir(), "drawio.url");
fs.writeFileSync(p, "[InternetShortcut]\r\nURL=" + process.argv[1] + "\r\n");
process.stdout.write(p);
' "$URL")
cmd.exe /c start "" "$TMPFILE"

After opening

Print the URL so the user can copy or share it, and confirm the local file path:

Opened in browser: <URL>
Local file: DIAGRAM.drawio

The .drawio file stays on disk so the user can re-edit it later, attach it elsewhere, or export it to an image format on demand.

URL length

The URL embeds the full compressed diagram in its hash fragment. Very large diagrams may hit browser URL length limits (typically ~32K–2MB depending on the browser). For complex diagrams that exceed the limit, fall back to writing the .drawio file and opening it locally.

draw.io CLI

The draw.io desktop app includes a command-line interface used for converting Mermaid to .drawio, applying ELK layouts (--layout), and exporting to PNG/SVG/PDF. All three require the desktop app to be installed.

Locating the CLI

First, detect the environment, then locate the CLI accordingly:

WSL2 (Windows Subsystem for Linux)

WSL2 is detected when /proc/version contains microsoft or WSL:

grep -qi microsoft /proc/version 2>/dev/null && echo "WSL2"

On WSL2, use the Windows draw.io Desktop executable via /mnt/c/...:

DRAWIO_CMD="/mnt/c/Program Files/draw.io/draw.io.exe"

Double-quote the path so the space in Program Files is treated as part of the path. Do not wrap it in backticks — in bash, backticks are command substitution, which would try to execute the binary at locate-time instead of storing its path.

If draw.io is installed in a non-default location, check common alternatives:

# Default install path
"/mnt/c/Program Files/draw.io/draw.io.exe"

# Per-user install (if the above does not exist)
"/mnt/c/Users/$WIN_USER/AppData/Local/Programs/draw.io/draw.io.exe"

macOS

/Applications/draw.io.app/Contents/MacOS/draw.io

Linux (native)

drawio   # typically on PATH via snap/apt/flatpak

Windows (native, non-WSL2)

"C:\Program Files\draw.io\draw.io.exe"

Use which drawio (or where draw.io on Windows) to check if it's on PATH before falling back to the platform-specific path.

Convert / layout / export commands

Convert Mermaid to .drawio:

drawio -x -f xml -o diagram.drawio diagram.mmd

Apply an ELK layout to XML (see ELK layout for XML):

drawio -x -f xml --layout verticalFlow -o diagram.drawio diagram.drawio

Export to an image format:

drawio -x -f <format> -e -b 10 -o "<output>" "<input.drawio>"

WSL2 export example:

"/mnt/c/Program Files/draw.io/draw.io.exe" -x -f png -e -b 10 -o "diagram.drawio.png" "diagram.drawio"

Key flags:

• -x / --export: export mode (also used for Mermaid conversion and layout passes)
• -f / --format: output format (xml, png, svg, pdf, jpg) — use xml to produce a .drawio from Mermaid or a layout pass
• --layout: run a layout before writing the output — an ELK preset name, the libavoid edge-routing pass, or a custom-layout JSON array
• --mermaid-image 1: convert Mermaid to a single static SVG image cell (the Mermaid source stays on the cell for re-editing) instead of an editable diagram — only when the user explicitly asks for a non-editable image cell
• -e / --embed-diagram: embed diagram XML in the output (PNG, SVG, PDF only)
• -o / --output: output file path
• -b / --border: border width around diagram (default: 0)
• -t / --transparent: transparent background (PNG only)
• -s / --scale: scale the diagram size
• --width / --height: fit into specified dimensions (preserves aspect ratio)
• -a / --all-pages: export all pages (PDF only)
• -p / --page-index: select a specific page (1-based)

Opening the result

WSL2 notes:

• wslpath -w <file> converts a WSL2 path (e.g. /home/user/diagram.drawio) to a Windows path (e.g. C:\Users\...). This is required because cmd.exe cannot resolve /mnt/c/... style paths.
• The empty string "" after start is required to prevent start from interpreting the filename as a window title.

WSL2 example:

cmd.exe /c start "" "$(wslpath -w diagram.drawio)"

File naming

• Use a descriptive filename based on the diagram content (e.g., login-flow, database-schema)
• Use lowercase with hyphens for multi-word names
• When authoring Mermaid, write it to a matching .mmd file, convert to .drawio, then delete the .mmd — the .drawio is the artifact
• For export, use double extensions: name.drawio.png, name.drawio.svg, name.drawio.pdf — this signals the file contains embedded diagram XML
• After a successful export, delete the intermediate .drawio file — the exported file contains the full diagram
• For url mode, keep the .drawio file (no double extension) — the URL is a view/edit handle and the local file is the persistent copy

XML format

A .drawio file is native mxGraphModel XML. When authoring as XML, generate it directly; Mermaid is converted to this same format by the CLI (-f xml), so both authoring routes end up as a native .drawio.

Basic structure

Every diagram must have this structure:

<mxGraphModel adaptiveColors="auto">
  <root>
    <mxCell id="0"/>
    <mxCell id="1" parent="0"/>
    <!-- Diagram cells go here with parent="1" -->
  </root>
</mxGraphModel>

• Cell id="0" is the root layer
• Cell id="1" is the default parent layer
• All diagram elements use parent="1" unless using multiple layers

(The example above uses an XML comment only to point out where cells go — never emit comments in real output; see XML well-formedness.)

XML reference

For the complete draw.io XML reference including common styles, edge routing, containers, layers, tags, metadata, dark mode colors, and XML well-formedness rules, fetch and follow the instructions at: shared/xml-reference.md

Troubleshooting

CRITICAL: XML well-formedness

• NEVER include ANY XML comments (<!-- -->) in the output. XML comments are strictly forbidden — they waste tokens, can cause parse errors, and serve no purpose in diagram XML.
• Escape special characters in attribute values: &, <, >, "
• Always use unique id values for each mxCell