# Drawio Impl Swimlanes
> Use when creating swimlane diagrams, cross-functional flowcharts, or pool/lane layouts in Draw.io. Prevents the #1 swimlane mistake: using absolute coordinates for children instead of container-relative coordinates. Covers horizontal and vertical swimlanes, nested lanes, header sizing, and cross-lane connections. Keywords: swimlane, pool, lane, cross-functional, container, startSize, horizontal, vertical, responsibility diagram, who does what, department process, cross-team workflow.
- Skill: `impertio-studio/drawio-impl-swimlanes` (Agent Skill, multi-file: 4 files)
- Install (CLI): `npx skillmds@latest add impertio-studio/drawio-impl-swimlanes`
- Raw SKILL.md: https://api.skillmd.com/api/skills/impertio-studio/drawio-impl-swimlanes/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Productivity
- License: MIT
- Author: Impertio-Studio (https://skillmd.com/u/impertio-studio)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/impertio-studio/drawio-impl-swimlanes
---
# Draw.io Swimlane Implementation
## Purpose
This skill enables correct generation of swimlane diagrams, cross-functional flowcharts, and pool/lane layouts in Draw.io mxGraph XML. It enforces the container-relative coordinate system and prevents the most common AI mistake: placing child shapes at absolute page coordinates instead of container-relative coordinates.
## Critical Rules (Memorize These)
1. **ALWAYS set `container=1`** in every swimlane and pool style — Without it, child shapes will NOT move with the lane when repositioned.
2. **ALWAYS use container-relative coordinates for children** — A child at `x="40" y="35"` is 40px from the lane's left edge and 35px from the lane's top edge (below the header). NEVER use absolute page coordinates.
3. **ALWAYS set `parent` to the container ID for child shapes** — A shape inside "lane1" MUST have `parent="lane1"`. NEVER set `parent="1"` for shapes that belong inside a container.
4. **ALWAYS set cross-lane edge `parent` to the common ancestor** — When an edge connects shapes in different lanes, set the edge's `parent` to the pool (the shared ancestor). NEVER set it to one of the individual lanes.
5. **ALWAYS include `collapsible=0`** on lanes — Without it, users can accidentally collapse lanes in the editor, hiding all contents.
6. **NEVER use absolute page coordinates for shapes inside a container** — This is the #1 swimlane mistake. Shapes will render at the wrong position and will NOT move with their parent lane.
## Container Hierarchy
Swimlane diagrams use a strict parent-child hierarchy:
```
Root (id="1")
Pool (container=1, parent="1") <-- absolute coordinates
Lane A (container=1, parent="pool") <-- relative to pool
Shape 1 (parent="lane_a") <-- relative to Lane A
Shape 2 (parent="lane_a") <-- relative to Lane A
Lane B (container=1, parent="pool") <-- relative to pool
Shape 3 (parent="lane_b") <-- relative to Lane B
Edge (parent="pool", source/target) <-- cross-lane edges on pool
```
## Pool Style
The pool is the outermost container that holds all lanes. Use `shape=table` for structured pool layouts:
```
shape=table;startSize=30;container=1;collapsible=0;childLayout=tableLayout;fixedRows=1;rowLines=0;fontStyle=1;strokeColor=#6c8ebf;fillColor=#dae8fc;
```
| Property | Value | Purpose |
|----------|-------|---------|
| `shape=table` | Required | Renders as a structured table container |
| `startSize` | `30` | Height of the pool header band (px) |
| `container` | `1` | REQUIRED — enables parent-child relationship |
| `collapsible` | `0` | Prevents accidental collapse |
| `childLayout` | `tableLayout` | Arranges child lanes as table rows |
| `fixedRows` | `1` | Locks lane row structure |
| `rowLines` | `0` | Hides row separator lines |
| `fontStyle` | `1` | Bold header text |
Alternative: use `swimlane;startSize=30;container=1;collapsible=0;` for a simpler pool without table layout.
## Lane Style
Each lane is a child container inside the pool:
```
swimlane;startSize=30;container=1;collapsible=0;horizontal=1;fillColor=#f5f5f5;strokeColor=#666666;fontStyle=1;
```
| Property | Value | Purpose |
|----------|-------|---------|
| `swimlane` | Required | Renders as a swimlane shape |
| `startSize` | `30` | Height of the lane header band (px) |
| `container` | `1` | REQUIRED — enables parent-child relationship |
| `collapsible` | `0` | Prevents accidental collapse |
| `horizontal` | `1` or `0` | Orientation (see next section) |
| `fontStyle` | `1` | Bold header text |
## Horizontal vs. Vertical Orientation
| Orientation | Style | Header Position | Flow Direction |
|-------------|-------|----------------|----------------|
| Horizontal lanes | `swimlane;horizontal=1;startSize=30;` | Left side (rotated text) | Left-to-right |
| Vertical lanes | `swimlane;horizontal=0;startSize=30;` | Top (horizontal text) | Top-to-bottom |
**Important:** The `horizontal` property controls the **header orientation**, NOT the lane stacking direction. `horizontal=0` means the header text is horizontal (rendered at the top), and lanes stack **side by side** — this is the most common layout for cross-functional flowcharts with top-to-bottom flow.
### When to Use Which
- **`horizontal=0` (vertical lanes, top-to-bottom flow):** Use for cross-functional flowcharts where the process flows downward and lanes represent departments/roles side by side. This is the DEFAULT for most business process diagrams.
- **`horizontal=1` (horizontal lanes, left-to-right flow):** Use when lanes stack vertically and the process flows left-to-right. Common for value stream maps and horizontal process flows.
## Header Sizing (startSize)
The `startSize` property controls the header band height (for `horizontal=0`) or width (for `horizontal=1`):
| startSize | Use Case |
|-----------|----------|
| `20` | Compact header, short labels |
| `30` | Default — fits single-line labels |
| `40` | Two-line labels or larger font |
| `50+` | Extended headers with descriptions |
**Coordinate impact:** The usable area for child shapes starts AFTER the header. For `startSize=30`, the first child shape's y-coordinate starts at y=0 relative to the lane (the header occupies the top 30px visually, but child y=0 is at the top-left of the content area after the header in practice). In Draw.io's XML, child y-coordinates are relative to the lane's top-left corner INCLUDING the header. Place children with y >= startSize to avoid overlap.
## Lane Geometry Rules
### Pool Positioning
The pool uses absolute page coordinates:
```xml
```
### Lane Positioning
Lanes use coordinates relative to the pool. The first lane starts at `y=startSize` (below the pool header):
```xml
```
**Width rule:** ALWAYS set lane width equal to pool width. Lanes span the full width of the pool.
**Height rule:** The sum of all lane heights plus the pool header startSize MUST equal the pool height:
- Pool height = startSize + lane1.height + lane2.height + ...
### Child Shape Positioning
Shapes inside lanes use coordinates relative to the lane's top-left corner:
```xml
```
Place children with `y >= startSize` of the lane to avoid overlapping the lane header.
## Cross-Lane Connections
Edges that connect shapes in different lanes MUST use the pool as their parent:
```xml
```
Edges that connect shapes within the SAME lane MAY use either the lane or the pool as parent. For consistency, ALWAYS use the pool as edge parent.
## Nested Lanes
Lanes can contain sub-lanes for finer granularity:
```xml
```
**Rule:** Sub-lane coordinates are relative to the parent lane. Sub-lane widths MUST equal the parent lane width.
## Auto-Expand Behavior
When `container=1` is set, Draw.io auto-expands the container if a child shape extends beyond its boundaries. To prevent unwanted expansion:
- ALWAYS size the pool and lanes large enough to contain all children.
- Add `resizable=1` to allow manual resizing in the editor.
- Add `recursiveResize=0` on the pool to prevent child lanes from auto-resizing when the pool resizes.
## Complete Example: 3-Lane Order Processing
```xml
```
This example demonstrates:
- 3 lanes (Sales, Warehouse, Finance) inside one pool
- 7 shapes across 3 lanes with container-relative coordinates
- Cross-lane connections with `parent="pool1"`
- Decision diamond with labeled Yes/No branches
- Document shape for invoice generation
- Consistent left-to-right flow within horizontal lanes
## Checklist: Before Outputting a Swimlane Diagram
1. Every pool and lane has `container=1` in its style.
2. Every lane has `collapsible=0` in its style.
3. Every child shape has `parent` set to its containing lane ID.
4. Every child shape uses coordinates relative to its lane (NOT absolute page coordinates).
5. Every cross-lane edge has `parent` set to the pool (common ancestor).
6. Lane widths equal the pool width.
7. Pool height = startSize + sum of all lane heights.
8. Child shapes have `y >= startSize` of their lane to avoid header overlap.
9. Both structural cells (`id="0"` and `id="1"`) are present.
10. All cell IDs are unique.
11. All edges have valid `source` and `target` attributes.
## Cross-References
- **XML fundamentals:** See `drawio-core-xml-format` for file structure and structural cells.
- **Style syntax:** See `drawio-syntax-styles` for the complete style property reference.
- **Connection details:** See `drawio-syntax-connections` for edge routing and waypoints.
- **Geometry:** See `drawio-core-geometry` for coordinate system and positioning.
- **Flowchart shapes:** See `drawio-impl-flowcharts` for ISO 5807 shapes used inside lanes.
## Reference Links
- [Complete Reference](references/methods.md)
- [Working Examples](references/examples.md)
- [Anti-Patterns](references/anti-patterns.md)