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drawio-impl-flowcharts

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Updated 10-15 22:17

About this skill

Draw.io Flowchart Implementation

Purpose

This skill enables correct generation of flowcharts, process flows, and decision trees in Draw.io mxGraph XML. It enforces ISO 5807 shape semantics and prevents the most common AI mistakes: wrong shapes for flowchart elements and missing decision branch labels.

Critical Rules (Memorize These)

  1. ALWAYS use rhombus for decisions — NEVER use a rectangle, rounded rectangle, or any other shape.
  2. ALWAYS label decision branches — Every edge leaving a decision MUST have a value attribute (e.g., value="Yes", value="No").
  3. ALWAYS use consistent flow direction — Pick one primary direction (top-to-bottom or left-to-right) and maintain it throughout the entire diagram.
  4. NEVER mix flow directions — A flowchart that flows both downward and leftward creates confusion and violates readability standards.
  5. ALWAYS include whiteSpace=wrap;html=1; in every shape style — Without it, text overflows and does not wrap.
  6. ALWAYS use rounded=1;arcSize=50; for terminators (Start/End) — This produces the ISO 5807 stadium/pill shape. NEVER use ellipse.

ISO 5807 Shape Reference

Shape Style Dimensions Purpose
Process rounded=0;whiteSpace=wrap;html=1; 140 x 60 Standard task or step (rectangle)
Decision rhombus;whiteSpace=wrap;html=1; 120 x 80 Yes/No or conditional branch (diamond)
Terminator rounded=1;whiteSpace=wrap;html=1;arcSize=50; 120 x 40 Start or End (stadium shape)
Data (I/O) shape=parallelogram;whiteSpace=wrap;html=1; 140 x 60 Input or output (parallelogram)
Document shape=document;whiteSpace=wrap;html=1; 140 x 60 Document output (wavy bottom)
Predefined Process shape=process;whiteSpace=wrap;html=1; 140 x 60 Subprocess reference (double-barred rectangle)
Manual Input shape=manualInput;whiteSpace=wrap;html=1; 140 x 60 User input (sloped top edge)
Preparation shape=hexagon;whiteSpace=wrap;html=1; 140 x 60 Setup or initialization step (hexagon)
Database shape=cylinder3;whiteSpace=wrap;html=1; 120 x 80 Data store (cylinder)

Decision Tree: Shape Selection

What does this step represent?
  A condition/question   --> rhombus (decision diamond)
  Start or End           --> rounded=1;arcSize=50 (terminator)
  A task/action          --> rounded=0 (process rectangle)
  Reading/writing data   --> shape=parallelogram (data I/O)
  Producing a document   --> shape=document
  Calling a subprocess   --> shape=process (predefined process)
  User entering data     --> shape=manualInput
  Setup/initialization   --> shape=hexagon (preparation)
  Storing to database    --> shape=cylinder3 (database)

Color Conventions

Use consistent colors to signal shape purpose:

Shape Type Fill Color Stroke Color
Terminator (Start) #d5e8d4 (light green) #82b366
Terminator (End) #f8cecc (light red) #b85450
Process #dae8fc (light blue) #6c8ebf
Decision #fff2cc (light yellow) #d6b656
Data I/O #e1d5e7 (light purple) #9673a6
Document #f5f5f5 (light gray) #666666
Database #e1d5e7 (light purple) #9673a6

Connection Patterns

Standard Edge Style

ALWAYS use endArrow=classic;html=1; as the base edge style for flowchart connections.

For clean orthogonal routing, add edgeStyle=orthogonalEdgeStyle;:

<mxCell id="e1" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;"
        edge="1" parent="1" source="step1" target="step2">
  <mxGeometry relative="1" as="geometry" />
</mxCell>

Decision Branch Edges

Decision branches MUST carry labels. The value attribute on the edge mxCell renders as an inline label:

<!-- Yes branch (continues downward in top-to-bottom flow) -->
<mxCell id="e_yes" value="Yes" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;"
        edge="1" parent="1" source="decision1" target="next_step">
  <mxGeometry relative="1" as="geometry" />
</mxCell>

<!-- No branch (exits to the side) -->
<mxCell id="e_no" value="No" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;"
        edge="1" parent="1" source="decision1" target="alt_step">
  <mxGeometry relative="1" as="geometry" />
</mxCell>

Multi-Way Branching

For decisions with more than two outcomes, use multiple labeled edges:

<mxCell id="e_low" value="Low" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;"
        edge="1" parent="1" source="priority_check" target="low_handler">
  <mxGeometry relative="1" as="geometry" />
</mxCell>
<mxCell id="e_med" value="Medium" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;"
        edge="1" parent="1" source="priority_check" target="med_handler">
  <mxGeometry relative="1" as="geometry" />
</mxCell>
<mxCell id="e_high" value="High" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;"
        edge="1" parent="1" source="priority_check" target="high_handler">
  <mxGeometry relative="1" as="geometry" />
</mxCell>

Layout Strategy

Top-to-Bottom (Default)

For top-to-bottom flow, use these coordinate guidelines:

  • Vertical spacing: 40px between shapes (bottom of shape N to top of shape N+1).
  • Horizontal center: Align the primary flow on a single x-axis center (e.g., x=200 for shapes of width 120-140).
  • Decision branches: The "Yes" (or primary) path continues downward. The "No" (or alternate) path exits to the right.
  • Merge points: When branches reconverge, place the merge target on the primary vertical axis.

Coordinate Calculation

For a top-to-bottom flowchart with center at x=260:

Shape 1 (terminator):  x=200, y=40,  width=120, height=40
Shape 2 (process):     x=190, y=120, width=140, height=60
Shape 3 (decision):    x=200, y=220, width=120, height=80
Shape 4a (Yes path):   x=190, y=340, width=140, height=60
Shape 4b (No path):    x=400, y=240, width=140, height=60
Shape 5 (terminator):  x=200, y=440, width=120, height=40

Left-to-Right Alternative

For left-to-right flow, rotate the coordinate logic: x increases for sequential steps, y changes for branches.

Complete Example: Order Processing Flowchart

<mxGraphModel>
  <root>
    <mxCell id="0" />
    <mxCell id="1" parent="0" />

    <!-- Start -->
    <mxCell id="start" value="Start" style="rounded=1;whiteSpace=wrap;html=1;arcSize=50;fillColor=#d5e8d4;strokeColor=#82b366;" vertex="1" parent="1">
      <mxGeometry x="200" y="40" width="120" height="40" as="geometry" />
    </mxCell>

    <!-- Receive Order -->
    <mxCell id="step1" value="Receive Order" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="1">
      <mxGeometry x="190" y="120" width="140" height="60" as="geometry" />
    </mxCell>

    <!-- Read Customer Data -->
    <mxCell id="io1" value="Read Customer&lt;br&gt;Data" style="shape=parallelogram;whiteSpace=wrap;html=1;fillColor=#e1d5e7;strokeColor=#9673a6;" vertex="1" parent="1">
      <mxGeometry x="190" y="220" width="140" height="60" as="geometry" />
    </mxCell>

    <!-- Validate Order -->
    <mxCell id="step2" value="Validate Order" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="1">
      <mxGeometry x="190" y="320" width="140" height="60" as="geometry" />
    </mxCell>

    <!-- Decision: Valid? -->
    <mxCell id="dec1" value="Order&lt;br&gt;Valid?" style="rhombus;whiteSpace=wrap;html=1;fillColor=#fff2cc;strokeColor=#d6b656;" vertex="1" parent="1">
      <mxGeometry x="200" y="420" width="120" height="80" as="geometry" />
    </mxCell>

    <!-- Decision: In Stock? -->
    <mxCell id="dec2" value="In Stock?" style="rhombus;whiteSpace=wrap;html=1;fillColor=#fff2cc;strokeColor=#d6b656;" vertex="1" parent="1">
      <mxGeometry x="200" y="540" width="120" height="80" as="geometry" />
    </mxCell>

    <!-- Process: Ship Order -->
    <mxCell id="step3" value="Ship Order" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="1">
      <mxGeometry x="190" y="660" width="140" height="60" as="geometry" />
    </mxCell>

    <!-- Generate Invoice (Document) -->
    <mxCell id="doc1" value="Generate&lt;br&gt;Invoice" style="shape=document;whiteSpace=wrap;html=1;fillColor=#f5f5f5;strokeColor=#666666;" vertex="1" parent="1">
      <mxGeometry x="190" y="760" width="140" height="60" as="geometry" />
    </mxCell>

    <!-- Update Database -->
    <mxCell id="db1" value="Update&lt;br&gt;Database" style="shape=cylinder3;whiteSpace=wrap;html=1;fillColor=#e1d5e7;strokeColor=#9673a6;" vertex="1" parent="1">
      <mxGeometry x="200" y="860" width="120" height="80" as="geometry" />
    </mxCell>

    <!-- End -->
    <mxCell id="end" value="End" style="rounded=1;whiteSpace=wrap;html=1;arcSize=50;fillColor=#f8cecc;strokeColor=#b85450;" vertex="1" parent="1">
      <mxGeometry x="200" y="980" width="120" height="40" as="geometry" />
    </mxCell>

    <!-- Error Handling: Reject Order -->
    <mxCell id="reject" value="Reject Order" style="rounded=0;whiteSpace=wrap;html=1;fillColor=#f8cecc;strokeColor=#b85450;" vertex="1" parent="1">
      <mxGeometry x="400" y="440" width="140" height="60" as="geometry" />
    </mxCell>

    <!-- Backorder Process (Predefined Process) -->
    <mxCell id="backorder" value="Backorder&lt;br&gt;Process" style="shape=process;whiteSpace=wrap;html=1;fillColor=#dae8fc;strokeColor=#6c8ebf;" vertex="1" parent="1">
      <mxGeometry x="400" y="560" width="140" height="60" as="geometry" />
    </mxCell>

    <!-- Connections -->
    <mxCell id="e1" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="start" target="step1">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e2" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="step1" target="io1">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e3" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="io1" target="step2">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e4" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="step2" target="dec1">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e5" value="Yes" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="dec1" target="dec2">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e6" value="No" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="dec1" target="reject">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e7" value="Yes" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="dec2" target="step3">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e8" value="No" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="dec2" target="backorder">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e9" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="step3" target="doc1">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e10" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="doc1" target="db1">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e11" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="db1" target="end">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e12" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="reject" target="end">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
    <mxCell id="e13" style="edgeStyle=orthogonalEdgeStyle;endArrow=classic;html=1;" edge="1" parent="1" source="backorder" target="step3">
      <mxGeometry relative="1" as="geometry" />
    </mxCell>
  </root>
</mxGraphModel>

This example demonstrates:

  • 12 shapes across 7 different shape types
  • 2 decision points with labeled branches
  • Consistent top-to-bottom flow
  • Side exits for alternate paths (No branches go right)
  • Reconvergence of branches back to the main flow
  • Proper use of Data I/O, Document, Database, and Predefined Process shapes

Auto-Layout Hints

When the flowchart is rendered via the Draw.io editor or MCP server, these mxGraphModel attributes improve layout:

<mxGraphModel dx="1422" dy="762" grid="1" gridSize="10" guides="1"
              tooltips="1" connect="1" arrows="1" fold="1" page="1"
              pageScale="1" pageWidth="1169" pageHeight="827">
  • grid="1" and gridSize="10" — Shapes snap to a 10px grid for alignment.
  • guides="1" — Snap guides appear when shapes align.
  • pageWidth="1169" and pageHeight="827" — A4 landscape page size.

Checklist: Before Outputting a Flowchart

  1. Every decision uses rhombus style.
  2. Every decision edge has a value label.
  3. All shapes include whiteSpace=wrap;html=1;.
  4. Terminators use rounded=1;arcSize=50;.
  5. Flow direction is consistent (no backtracking).
  6. Cell IDs are unique.
  7. Both structural cells (id="0" and id="1") are present.
  8. All edges have source and target attributes pointing to valid cell IDs.

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.

Reference Links