FlowForge — Draw.io Diagram Skill

Generate professional diagrams as draw.io XML files. Supports 13 diagram types: flows, comparisons, layer stacks, cycles, trees, hub-and-spoke, columns, matrices, funnels, timelines, sequence diagrams, and swimlanes.

Usage

/FlowForge "OAuth 2.0 authorization code flow"
/FlowForge path/to/design-doc.md
/FlowForge "CI/CD pipeline" --type loop
/FlowForge "Monolith vs Microservices" --type compare --theme morandi
/FlowForge "System Architecture" --lang en

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Workflow

Step 1: Understand & Propose (one confirmation, not three)

If given a document: read it fully, identify 1–3 places that benefit from a diagram, and for each note the insert position, the topic (one sentence), and the recommended type (see Diagram Type Reference).

If given a concept directly: identify the core message and pick the type via the Selection Guide.

Then present one combined proposal and ask for confirmation once. The proposal contains:

• Diagram type and theme (default: tech-blue; other options: morandi, mint, terracotta, indigo)
• An ASCII sketch: all nodes with labels, arrow directions and labels, grouping, color-role tags, layout direction

Example sketch:

Direction: left-to-right | Nodes: 4 | Type: flow | Theme: tech-blue

[primary] Code Commit  →  [process] Build  →  [process] Test  →  [accent] Deploy
                                                    ↓ (fail)
                                              [error] Alert

Skip the confirmation entirely when the request already pins everything down (user gave --type/--theme or an unambiguous description), or when no human can respond (subagent, batch, CI). In that case proceed with defaults and state your assumptions in the final report.

Step 2: Generate draw.io XML

1. Read references/layouts.md — the layout algorithm for the chosen type — and compute all coordinates from its formulas
2. Apply theme colors from themes.md
3. Use element templates from xml-reference.md
4. For an unfamiliar type, read the matching example file listed in examples.md

Step 3: Validate (mandatory)

python3 {skill_dir}/scripts/validate.py <file.drawio> --theme <theme>

This deterministically checks: XML well-formedness, unique ids, dangling arrow references, orthogonal edge style, canvas bounds, node overlap, z-order (containers before children), font sizes, text-fit estimates, and theme color compliance. Fix every ERROR and re-run until clean. WARNs are heuristics — judge each one, fix the real ones.

Step 4: Visual self-check (when draw.io CLI is available)

bash {skill_dir}/scripts/render.sh <file.drawio>   # writes a .png next to the file

If the script reports draw.io is not installed, skip this step (the user can enable it once with brew install --cask drawio). Otherwise Read the PNG and inspect it with fresh eyes: text overflowing nodes, crowded regions, arrows colliding with nodes, color rhythm, overall balance. Fix and re-render until it looks right — this catches what rules can't.

Step 5: Save & Deliver

Save the .drawio file to the output directory (see Configuration). After saving, report:

• File path (and the rendered PNG path if Step 4 ran)
• How to open: draw.io desktop app or https://app.diagrams.net

Iteration

If the user wants changes after viewing:

1. Read the current .drawio file
2. Modify the XML per feedback
3. Save as {name}_v2.drawio (preserve previous version), then re-run Steps 3–4

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Configuration

Optional per-project config file ./.flowforge.json (in the working directory, never inside the skill directory — the skill directory may be read-only or shared across projects):

{
  "defaultTheme": "tech-blue",
  "outputDir": "./diagrams",
  "language": "auto"
}

If the file is absent, use exactly these defaults — do not interview the user. "language": "auto" means match the user's language; technical abbreviations (API, LLM, CI/CD) stay in English regardless. Per-invocation flags (--theme, --lang) override config.

---

Diagram Type Reference

Core Types

Type	Code	Best For	Example
Linear Flow	flow	Sequential steps A→B→C	API call flow, data pipeline
Vertical Flow	flow-vertical	Top-down processes	Decision process, approval chain
Comparison	compare	A vs B side by side	Traditional vs AI approach
Layer Stack	layers	Tech stack, tiers	System architecture layers
Cycle	loop	Iterative processes	ML training loop, CI/CD
Tree	tree	Hierarchies, taxonomies	Org chart, decision tree
Hub & Spoke	hub	Core concept + branches	Product feature map

Extended Types

Type	Code	Best For
Parallel Columns	columns	3+ parallel concepts
Matrix	matrix	Multi-dimension comparison
Funnel	funnel	Filtering, conversion
Timeline	timeline	Version evolution, history
Sequence	sequence	Component interactions
Swimlane	swimlane	Cross-role processes (who does what)

Selection Guide

Content Pattern	Recommended Type
Sequential steps	flow or flow-vertical
Two things compared	compare
3+ parallel concepts	columns or hub
Layered system	layers
Iterative/cyclical process	loop
One core, many branches (incl. mind-map style)	hub or tree
Components communicating	sequence
Change over time	timeline
Multi-criteria evaluation	matrix
Progressive filtering	funnel
Steps owned by different roles/systems	swimlane

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Color Usage Principles

This is the most important section for visual quality.

The 4+6 Rule

Each theme has 4 base colors (primary, process, accent, neutral) and 6 extended colors (success, warning, error, secondary, storage, group). The primary family should always dominate; the amount of non-primary accents scales with diagram size.

Color Budget by Diagram Size

Node Count	Target Colors	Guideline
3-5 nodes	2-3 colors	Primary family dominates. At most 1 accent node.
6-8 nodes	3-4 colors	Primary ~60%. Add 1-2 non-primary at semantic turning points.
9+ nodes	4-5 colors	Primary ~50%. Distribute 2-3 non-primary for visual rhythm.

6+ colors almost always looks bad regardless of diagram size.

Color Assignment Strategy

1. Primary dominates — primary and process cover the largest visual area and the biggest nodes.
2. Accent is a scalpel, not a paintbrush — at most 1-2 key highlights, never the largest node.
3. Scale with length — a 4-node flow with 2 colors looks clean; a 9-node flow with 2 colors is a monotonous wall. Add non-primary colors at natural semantic boundaries to create rhythm.
4. 3-consecutive guideline — if you spot 4+ adjacent same-color nodes, promote the most semantically distinctive one.
5. Distribute spatially — non-primary nodes spread across the diagram, not clustered in one region.

Semantic Color Heuristics

Node Type	Recommended Color
User input / starting point	primary
Standard processing step	process
Decision / branching point	warning or accent
Domain-specific / translation step	secondary
Key transformation / highlight	accent
Data source / external system	neutral
Error path / fallback	accent or error
Successful output / endpoint	success or primary
Database / storage	storage

Good/bad worked examples of color rhythm are at the bottom of themes.md.

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Design Principles

1. Narrative titles — Use "How OAuth 2.0 Authorizes a User" not "OAuth 2.0 Diagram".
2. Bilingual labels — Use the user's language. Technical abbreviations (API, LLM, CI/CD) stay in English regardless.
3. Orthogonal flow arrows — Every arrow between nodes includes edgeStyle=orthogonalEdgeStyle; so it runs horizontal/vertical only. Exception: decorative connectors with endArrow=none (hub rays, timeline axis/ticks) may run straight.

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Gotchas — Common Failure Points

The validator (Step 3) catches most geometry/reference mistakes after the fact, but knowing these saves a fix cycle:

1. Rich node title duplication — the title lives in a separate text cell; keep value="" on the background rect or it renders twice.
2. Arrow ignores exit/entry points — always specify exitX/exitY/entryX/entryY; otherwise draw.io auto-routes, usually badly.
3. HTML entities in value attributes — value is HTML inside an XML attribute: < > &, and • for bullets. One missing escape breaks the whole file (validator: parse error).
4. Filled boxes drawn after their children hide them — define lane bands and any filled container BEFORE the nodes inside them (validator: z-order check).
5. Canvas too small — compute pageWidth/pageHeight from the layout formulas: max(x + w) + CANVAS_PAD (validator: bounds check).
6. Forgetting parent="1" — every content element needs it unless intentionally grouped (validator: parent check).
7. Diamond text overflow — rhombus shapes have ~60% usable width; keep labels to 2-3 short words, font 11.
8. Snake layout wrap arrows — the wrap-around arrow exits the BOTTOM of the last node in a row and enters the TOP of the next row's first node, not sideways.
9. Cycle return arrow — in loop diagrams, route the last→first arrow around the outside of the rectangle, never through the center.
10. Off-by-one in widths — n nodes have n-1 gaps: canvas width = PAD×2 + n×NODE_W + (n-1)×GAP_H (validator: bounds/overlap).
11. Branch/merge arrows go diagonal — when exit/entry points aren't aligned, only edgeStyle=orthogonalEdgeStyle; keeps them orthogonal — include it in every flow arrow (validator: style check).

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Supporting Files

Read them when the workflow step calls for them — don't load everything upfront.

File	When to read
references/layouts.md	Step 2, before computing coordinates — global constants + all 13 layout algorithms
themes.md	Step 2, when applying colors — 5 themes × 10 semantic colors + 7 text colors, color-rhythm examples
xml-reference.md	Step 2, when writing XML — canvas boilerplate, element templates, arrow direction table
examples.md	Step 2 — coordinate-calculation walkthroughs + index of example files
scripts/validate.py	Step 3 — run on every generated file (don't read it, run it)
scripts/render.sh	Step 4 — export PNG for the visual self-check

Example .drawio files (in examples/)

Real, working files to read as reference when generating a similar type:

• examples/flow-cicd.drawio — Linear flow, 4 nodes, tech-blue
• examples/compare-monolith-vs-micro.drawio — Comparison, 2 columns × 3 rows, morandi
• examples/loop-ml-training.drawio — Cycle, 4 nodes clockwise, mint
• examples/tree-storage-decision.drawio — Decision tree with diamonds, mint
• examples/hub-agent-capabilities.drawio — Hub & spoke, 6 spokes with rays, indigo
• examples/timeline-llm-history.drawio — Timeline with axis + ticks, terracotta