Drawio Skill

Draw.io Diagrams

Overview

Generate .drawio XML files and export to PNG/SVG/PDF/JPG locally using the native draw.io desktop app CLI.

Supported formats: PNG, SVG, PDF, JPG — no browser automation needed.

PNG, SVG, and PDF exports support --embed-diagram (-e) — the exported file contains the full diagram XML, so opening it in draw.io recovers the editable diagram. Use double extensions (name.drawio.png) to signal embedded XML.

Bundled resources

When the workflow references one of these, read it on demand — none of them need to be in context up front.

Prerequisites

The draw.io desktop app must be installed and the CLI accessible:

macOS sandbox / sandbox isolation note (e.g., codex.app): In some sandboxed macOS environments, invoking the draw.io desktop CLI (even draw.io --version) can crash the draw.io process or produce no output. If that happens, treat the CLI as unavailable in this sandbox isolation — do not keep retrying inside the sandbox. Prefer a non-sandboxed host environment (outside sandbox isolation) for any CLI export work, or use the browser fallback / XML-only outputs.

# macOS (Homebrew — recommended; CLI binary is `drawio`, not `draw.io`)
brew install --cask drawio
drawio --version

# macOS (full path if not in PATH)
/Applications/draw.io.app/Contents/MacOS/draw.io --version

# Windows
"C:\Program Files\draw.io\draw.io.exe" --version

# Linux
draw.io --version

Install draw.io desktop if missing:

• macOS: brew install --cask drawio or download from https://github.com/jgraph/drawio-desktop/releases
• Windows: download installer from https://github.com/jgraph/drawio-desktop/releases
• Linux: download .deb/.rpm from https://github.com/jgraph/drawio-desktop/releases — do not use snap (AppArmor sandbox denies secrets/keyring on servers, causes crash)

Workflow

Before starting the workflow, assess whether the user's request is specific enough. If key details are missing, ask 1-3 focused questions:

• Diagram type — which preset? (ERD, UML, Sequence, Architecture, ML/DL, Flowchart, or general)
• Output format — PNG (default), SVG, PDF, or JPG?
• Output location — default is the user's working dir; honor any explicit path the user gives (e.g. "put it in ./artifacts/"). Don't ask if they didn't mention one.
• Scope/fidelity — how many components? Any specific technologies or labels?

Skip clarification if the request already specifies these details or is clearly simple (e.g., "draw a flowchart of X").

Step 0 — Resolve active preset. Determine which (if any) user-defined style preset applies to this generation.

• Scan the user's message for a phrase that clearly names a style preset: "use my <name> style", "with my <name> style", "in <name> mode", "in the style of <name>". A bare with <name> does not count — "draw a diagram with redis" names a component, not a style. If a clear match is found → active preset = <name>.
• Else, check ~/.drawio-skill/styles/ for any file with "default": true. If found → active preset = that one.
• Else → no preset active; fall through to the built-in color/shape/edge conventions for the rest of the workflow.

Load the preset JSON from ~/.drawio-skill/styles/<name>.json, falling back to <this-skill-dir>/styles/built-in/<name>.json. If the named preset exists in neither location, tell the user the name is unknown, list the available presets (user dir + built-in), and stop — do not silently fall back to defaults.

When a preset loads successfully, mention it in the first line of the reply: "Using preset <name> (confidence: <level>)." See the Applying a preset subsection below for how the preset changes color/shape/edge/font decisions.

1. Check deps — verify draw.io --version succeeds; note platform for correct CLI path
2. Plan — identify shapes, relationships, layout (LR or TB), group by tier/layer
3. Generate — write .drawio XML file to disk. Default output dir is the user's working dir; if the user specified an output path or directory (e.g. ./artifacts/, docs/images/), use that instead — mkdir -p the target dir first. Apply the same dir choice to PNG/SVG/PDF exports in steps 4 and 7.
4. Export draft — run CLI to produce a preview PNG. Do NOT pass -e at this step — the embedded zTXt mxGraphModel chunk it adds causes vision APIs (Claude included) to return 400 "Could not process image" in step 5. Save the clean preview as <name>.png (single extension). Embedding is for the final export only (step 7).
5. Self-check — use the agent's built-in vision capability to read the exported PNG, catch obvious issues, auto-fix before showing user (requires a vision-enabled model such as Claude Sonnet/Opus). If reading the PNG returns a 400 / "Could not process image" error, you almost certainly exported with -e by mistake — re-export without -e and retry once. If it still fails, skip self-check and continue to step 6.
6. Review loop — show image to user, collect feedback, apply targeted XML edits, re-export, repeat until approved
7. Final export — re-export the approved version to all requested formats. Use -e here (PNG/SVG/PDF) so the deliverable stays editable in draw.io; save as <name>.drawio.png to signal embedded XML. For PNG with -e, run python3 <this-skill-dir>/scripts/repair_png.py <name>.drawio.png immediately after — draw.io's CLI truncates the IEND chunk in -e PNG output (8 bytes missing), producing a corrupt file that vision APIs and strict PNG decoders reject (issue #8). Report file paths.

If draw.io --version crashes or prints nothing (common in restricted macOS sandbox isolation like codex.app):

• Do not keep retrying CLI invocations inside the sandbox.
• Skip steps 4, 5, 6, and 7 (CLI export + PNG-based review) and use Browser fallback (scripts/encode_drawio_url.py) or deliver the .drawio XML only.
• If the user needs PNG/SVG/PDF outputs, ask them to run the export commands in a non-sandboxed host environment (outside sandbox isolation) and share the resulting files.

Escalation rule:

• If the binary exists on PATH (or known app path exists) but execution fails with abnormal exit, empty output, Electron startup failure, display/session error, or likely sandbox restriction, prefer one escalated retry before falling back.
• If the binary is missing entirely, do not escalate just to search more aggressively; go to install guidance or fallback.

Step 5: Self-Check

After exporting the draft PNG, use the agent's vision capability (e.g., Claude's image input) to read the image and check for these issues before showing the user. If the agent does not support vision, skip self-check and show the PNG directly.

Important: the draft PNG read here must have been exported without -e. Draw.io's -e flag emits a PNG with a truncated IEND chunk (8 bytes of type+CRC missing) that the Anthropic vision API rejects with 400 "Could not process image" (issue #8). The simplest fix for the preview step is to skip -e entirely; the final export in step 7 keeps -e and runs the repair snippet. If you see the 400 error here, re-export without -e and retry once; if it still fails (any other reason), skip self-check and proceed to step 6.

• Max 2 self-check rounds — if issues remain after 2 fixes, show the user anyway
• Re-export after each fix and re-read the new PNG

Step 6: Review Loop

After self-check, show the exported image and ask the user for feedback.

Targeted edit rules — for each type of feedback, apply the minimal XML change:

Rules:

• For single-element changes: edit existing XML in place — preserves layout tuning from prior iterations
• For layout-wide changes (e.g., swap LR↔TB, "start over"): regenerate full XML
• Overwrite the same {name}.png (no -e) each iteration — do not create v1, v2, v3 files. -e is reserved for the final export in step 7.
• After applying edits, re-export and show the updated image
• Loop continues until user says approved / done / LGTM
• Safety valve: after 5 iteration rounds, suggest the user open the .drawio file in draw.io desktop for fine-grained adjustments

Step 7: Final Export

Once the user approves:

• Export to all requested formats (PNG, SVG, PDF, JPG) — default to PNG if not specified
• Report file paths for both the .drawio source file and exported image(s)
• Auto-launch: offer to open the .drawio file in draw.io desktop for fine-tuning — open diagram.drawio (macOS), xdg-open (Linux), start (Windows)
• Confirm files are saved and ready to use

Style Presets

A style preset is a named JSON file capturing a user's visual preferences (palette, shapes, font, edges). When active, it fully replaces the built-in color/shape conventions in this skill.

Lookup order when SKILL.md's step 0.5 resolves a preset name:

1. ~/.drawio-skill/styles/<name>.json — user presets (survive git pull)
2. <this-skill-dir>/styles/built-in/<name>.json — shipped built-ins (default, corporate, handdrawn)

Always lowercase the user-provided name before any file operation — the schema enforces lowercase.

For everything else — Learn flow (extracting a preset from a file), management ops (list/default/delete/rename), application rules (color lookup, shape keywords, edges, fonts, extras, interaction with diagram-type presets), and validation — read references/style-presets.md. It's only needed when the user invokes those flows or when an active preset must be applied to the current generation.

Draw.io XML Structure

File skeleton

<?xml version="1.0" encoding="UTF-8"?>
<mxfile host="drawio" version="26.0.0">
  <diagram name="Page-1">
    <mxGraphModel>
      <root>
        <mxCell id="0" />
        <mxCell id="1" parent="0" />
        <!-- user shapes start at id="2" -->
      </root>
    </mxGraphModel>
  </diagram>
</mxfile>

Rules:

• id="0" and id="1" are required root cells — never omit them
• User shapes start at id="2" and increment sequentially
• All shapes have parent="1" (unless inside a container — then use container's id)
• All text uses html=1 in style for proper rendering
• Never use -- inside XML comments — it's illegal per XML spec and causes parse errors
• Escape special characters in attribute values: &, <, >, "
• Multi-line text in labels: use 
 for line breaks inside value attributes (not literal \n). Example: value="Line 1
Line 2"

Shape types (vertex)

Required properties

<!-- Rectangle / rounded box -->
<mxCell id="2" value="Label" style="rounded=1;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="1">
  <mxGeometry x="100" y="100" width="160" height="60" as="geometry" />
</mxCell>

<!-- Cylinder (database) -->
<mxCell id="3" value="DB" style="shape=cylinder3;whiteSpace=wrap;html=1;fillColor=#f5f5f5;strokeColor=#666666;fontColor=#333333;" vertex="1" parent="1">
  <mxGeometry x="350" y="100" width="120" height="80" as="geometry" />
</mxCell>

<!-- Diamond (decision) -->
<mxCell id="4" value="Check?" style="rhombus;whiteSpace=wrap;html=1;fillColor=#fff2cc;strokeColor=#d6b656;" vertex="1" parent="1">
  <mxGeometry x="100" y="220" width="160" height="80" as="geometry" />
</mxCell>

Containers and groups

For architecture diagrams with nested elements, use draw.io's parent-child containment — do not just place shapes on top of larger shapes.

Key rules:

• Add pointerEvents=0; to container styles that should not capture connections between children
• Children set parent="containerId" and use coordinates relative to the container

<!-- Swimlane container -->
<mxCell id="svc1" value="User Service" style="swimlane;startSize=30;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="1">
  <mxGeometry x="100" y="100" width="300" height="200" as="geometry"/>
</mxCell>
<!-- Child inside container — coordinates relative to parent -->
<mxCell id="api1" value="REST API" style="rounded=1;whiteSpace=wrap;html=1;" vertex="1" parent="svc1">
  <mxGeometry x="20" y="40" width="120" height="60" as="geometry"/>
</mxCell>
<mxCell id="db1" value="Database" style="shape=cylinder3;whiteSpace=wrap;html=1;" vertex="1" parent="svc1">
  <mxGeometry x="160" y="40" width="120" height="60" as="geometry"/>
</mxCell>

Connector (edge)

CRITICAL: Every edge mxCell must contain a <mxGeometry relative="1" as="geometry" /> child element. Self-closing edge cells (<mxCell ... edge="1" ... />) are invalid and will not render. Always use the expanded form.

<!-- Directed arrow — always include rounded, orthogonalLoop, jettySize for clean routing -->
<mxCell id="10" value="" style="edgeStyle=orthogonalEdgeStyle;rounded=1;orthogonalLoop=1;jettySize=auto;html=1;" edge="1" parent="1" source="2" target="3">
  <mxGeometry relative="1" as="geometry" />
</mxCell>

<!-- Arrow with label + explicit entry/exit points to control direction -->
<mxCell id="11" value="HTTP/REST" style="edgeStyle=orthogonalEdgeStyle;rounded=1;orthogonalLoop=1;jettySize=auto;html=1;exitX=0.5;exitY=1;exitDx=0;exitDy=0;entryX=0.5;entryY=0;entryDx=0;entryDy=0;" edge="1" parent="1" source="2" target="4">
  <mxGeometry relative="1" as="geometry" />
</mxCell>

<!-- Arrow with waypoints — use when edge must route around other shapes -->
<mxCell id="12" value="" style="edgeStyle=orthogonalEdgeStyle;rounded=1;orthogonalLoop=1;jettySize=auto;html=1;" edge="1" parent="1" source="3" target="5">
  <mxGeometry relative="1" as="geometry">
    <Array as="points">
      <mxPoint x="500" y="50" />
    </Array>
  </mxGeometry>
</mxCell>

Edge style rules:

• Animated connectors: add flowAnimation=1; to any edge style to show a moving dot animation along the arrow. Works in SVG export and draw.io desktop — ideal for data-flow and pipeline diagrams. Example: style="edgeStyle=orthogonalEdgeStyle;flowAnimation=1;rounded=1;..."
• Always include rounded=1;orthogonalLoop=1;jettySize=auto — these enable smart routing that avoids overlaps
• Pin exitX/exitY/entryX/entryY on every edge when a node has 2+ connections — distributes lines across the shape perimeter
• Add <Array as="points"> waypoints when an edge must detour around an intermediate shape
• Leave room for arrowheads: the final straight segment between the last bend and the target shape must be ≥20px long. If too short, the arrowhead overlaps the bend and looks broken. Fix by increasing node spacing or adding explicit waypoints

Distributing connections on a shape

When multiple edges connect to the same shape, assign different entry/exit points to prevent stacking:

Rule: if a shape has N connections on one side, space them evenly (e.g., 3 connections on bottom → exitX = 0.25, 0.5, 0.75)

Color palette (fillColor / strokeColor)

Used only when no preset is active (see "Applying a preset" above).

Layout tips

Spacing — scale with complexity:

Routing corridors: between shape rows/columns, leave an extra ~80px empty corridor where edges can route without crossing shapes. Never place a shape in a gap that edges need to traverse.

Grid alignment: snap all x, y, width, height values to multiples of 10 — this ensures shapes align cleanly on draw.io's default grid and makes manual editing easier.

General rules:

• Plan a grid before assigning x/y coordinates — sketch node positions on paper/mentally first
• Group related nodes in the same horizontal or vertical band
• Use swimlane cells for logical grouping with visible borders
• Place heavily-connected "hub" nodes centrally so edges radiate outward instead of crossing
• To force straight vertical connections, pin entry/exit points explicitly on edges: exitX=0.5;exitY=1;exitDx=0;exitDy=0;entryX=0.5;entryY=0;entryDx=0;entryDy=0
• Always center-align a child node under its parent (same center x) to avoid diagonal routing
• Event bus pattern: place Kafka/bus nodes in the center of the service row, not below — services on either side can reach it with short horizontal arrows (exitX=1 left side, exitX=0 right side), eliminating all line crossings
• Horizontal connections (exitX=1 or exitX=0) never cross vertical nodes in the same row; use them for peer-to-peer and publish connections

Avoiding edge-shape overlap:

• Before finalizing coordinates, trace each edge path mentally — if it must cross an unrelated shape, either move the shape or add waypoints
• For tree/hierarchical layouts: assign nodes to layers (rows), connect only between adjacent layers to minimize crossings
• For star/hub layouts: place the hub center, satellites around it — edges stay short and radial
• When an edge must span multiple rows/columns, route it along the outer corridor, not through the middle of the diagram

Export

Commands

There are two export modes:

• Preview / self-check (step 4 of the workflow) — no -e. Output diagram.png. Required for vision self-check; using -e here triggers a 400 "Could not process image" error from the vision API (issue #8).
• Final / deliverable (step 7) — pass -e. Output diagram.drawio.png. The embedded XML keeps the file editable in draw.io.

# Preview PNG (use this in step 4, before self-check) — NO -e
draw.io -x -f png -s 2 -o diagram.png input.drawio

# Final PNG (step 7, after user approval) — WITH -e, double extension
draw.io -x -f png -e -s 2 -o diagram.drawio.png input.drawio

# macOS — full path (if not in PATH); preview / final variants
/Applications/draw.io.app/Contents/MacOS/draw.io -x -f png -s 2 -o diagram.png input.drawio
/Applications/draw.io.app/Contents/MacOS/draw.io -x -f png -e -s 2 -o diagram.drawio.png input.drawio

# Windows
"C:\Program Files\draw.io\draw.io.exe" -x -f png -e -s 2 -o diagram.drawio.png input.drawio

# Linux (headless — requires xvfb-run; on servers add HOME and --disable-gpu)
export HOME=${HOME:-/tmp}
xvfb-run -a --server-args="-screen 0 1280x1024x24" \
  draw.io -x -f png -e -s 2 -o diagram.drawio.png input.drawio --disable-gpu
# Running as root (CI / Docker)? Append --no-sandbox AT THE END (placing it earlier makes drawio treat it as the input filename)

# SVG export (final — -e is safe; SVG is text)
draw.io -x -f svg -e -o diagram.svg input.drawio

# PDF export (final)
draw.io -x -f pdf -e -o diagram.pdf input.drawio

# Custom output directory (e.g. CI artifacts dir) — create if missing, then export there
mkdir -p ./artifacts && draw.io -x -f png -e -s 2 -o ./artifacts/diagram.drawio.png input.drawio

Post-export PNG repair (required after -e PNG export)

draw.io CLI truncates the IEND chunk when emitting -e PNGs — the file ends with the 4-byte IEND length field but the IEND type + CRC (8 bytes) are missing. Result: vision APIs return 400 "Could not process image" and strict PNG decoders error out. SVG/PDF are unaffected.

Run this immediately after every -e PNG export:

python3 <this-skill-dir>/scripts/repair_png.py diagram.drawio.png

The script's endswith(IEND) guard makes it a no-op once draw.io fixes the bug upstream — safe to run unconditionally.

Key flags:

• -x — export mode (required)
• -f — format: png, svg, pdf, jpg
• -e — embed diagram XML in output (PNG, SVG, PDF) — exported file remains editable in draw.io. Skip for the preview PNG used in step 5 self-check — -e PNGs have a truncated IEND chunk that vision APIs reject (issue #8). For final PNG export, keep -e and run scripts/repair_png.py (see Post-export PNG repair). SVG/PDF unaffected.
• -s — scale: 1, 2, 3 (2 recommended for PNG)
• -o — output file path; accepts any directory (e.g. ./artifacts/diagram.drawio.png) — mkdir -p the target dir first. Use .drawio.png double extension when embedding.
• -b — border width around diagram (default: 0, recommend 10)
• -t — transparent background (PNG only)
• --page-index 0 — export specific page (default: all)

Browser fallback (no CLI needed)

When the draw.io desktop CLI is unavailable, generate a client-side viewer URL:

python3 <this-skill-dir>/scripts/encode_drawio_url.py input.drawio

Prints a https://viewer.diagrams.net/... URL with the diagram XML deflate-compressed and base64-encoded into the URL fragment. The fragment (after #) is never sent to the server, so nothing is uploaded — the diagram opens client-side for viewing and editing. Useful when the user cannot install the desktop app.

Fallback chain

When tools are unavailable, degrade gracefully:

Checking if draw.io is in PATH

# Try short command first
if command -v draw.io &>/dev/null; then
  DRAWIO="draw.io"
elif [ -f "/Applications/draw.io.app/Contents/MacOS/draw.io" ]; then
  DRAWIO="/Applications/draw.io.app/Contents/MacOS/draw.io"
else
  echo "draw.io not found — install from https://github.com/jgraph/drawio-desktop/releases"
fi

Common Mistakes

When something looks wrong (export fails, vision rejects a PNG, layout broken, edges misroute), see references/troubleshooting.md for a row-by-row mistake → fix table.

Diagram Type Presets

When the user requests a specific diagram type, read references/diagram-types.md for the matching preset (shapes, edges, layout direction). Pick by user phrasing:

The diagram-type preset sets structural style keywords. If a user style preset is also active (see ## Style Presets), keep the structural keywords and layer color/font/edge/extras on top — read references/style-presets.md → "Interaction with diagram-type presets" for the merge rules.