concept-diagrams

What this skill does

# Concept Diagrams

Generate production-quality SVG diagrams with a unified flat, minimal design system. Output is a single self-contained HTML file that renders identically in any modern browser, with automatic light/dark mode.

## Scope

**Best suited for:**
- Physics setups, chemistry mechanisms, math curves, biology
- Physical objects (aircraft, turbines, smartphones, mechanical watches, cells)
- Anatomy, cross-sections, exploded layer views
- Floor plans, architectural conversions
- Narrative journeys (lifecycle of X, process of Y)
- Hub-spoke system integrations (smart city, IoT networks, electricity grids)
- Educational / textbook-style visuals in any domain
- Quantitative charts (grouped bars, energy profiles)

**Look elsewhere first for:**
- Dedicated software / cloud infrastructure architecture with a dark tech aesthetic (consider `architecture-diagram` if available)
- Hand-drawn whiteboard sketches (consider `excalidraw` if available)
- Animated explainers or video output (consider an animation skill)

If a more specialized skill is available for the subject, prefer that. If none fits, this skill can serve as a general-purpose SVG diagram fallback — the output will carry the clean educational aesthetic described below, which is a reasonable default for almost any subject.

## Workflow

1. Decide on the diagram type (see Diagram Types below).
2. Lay out components using the Design System rules.
3. Write the full HTML page using `templates/template.html` as the wrapper — paste your SVG where the template says `<!-- PASTE SVG HERE -->`.
4. Save as a standalone `.html` file (for example `~/my-diagram.html` or `./my-diagram.html`).
5. User opens it directly in a browser — no server, no dependencies.

Optional: if the user wants a browsable gallery of multiple diagrams, see "Local Preview Server" at the bottom.

Load the HTML template:
```
skill_view(name="concept-diagrams", file_path="templates/template.html")
```

The template embeds the full CSS design system (`c-*` color classes, text classes, light/dark variables, arrow marker styles). The SVG you generate relies on these classes being present on the hosting page.

---

## Design System

### Philosophy

- **Flat**: no gradients, drop shadows, blur, glow, or neon effects.
- **Minimal**: show the essential. No decorative icons inside boxes.
- **Consistent**: same colors, spacing, typography, and stroke widths across every diagram.
- **Dark-mode ready**: all colors auto-adapt via CSS classes — no per-mode SVG.

### Color Palette

9 color ramps, each with 7 stops. Put the class name on a `<g>` or shape element; the template CSS handles both modes.

| Class      | 50 (lightest) | 100     | 200     | 400     | 600     | 800     | 900 (darkest) |
|------------|---------------|---------|---------|---------|---------|---------|---------------|
| `c-purple` | #EEEDFE | #CECBF6 | #AFA9EC | #7F77DD | #534AB7 | #3C3489 | #26215C |
| `c-teal`   | #E1F5EE | #9FE1CB | #5DCAA5 | #1D9E75 | #0F6E56 | #085041 | #04342C |
| `c-coral`  | #FAECE7 | #F5C4B3 | #F0997B | #D85A30 | #993C1D | #712B13 | #4A1B0C |
| `c-pink`   | #FBEAF0 | #F4C0D1 | #ED93B1 | #D4537E | #993556 | #72243E | #4B1528 |
| `c-gray`   | #F1EFE8 | #D3D1C7 | #B4B2A9 | #888780 | #5F5E5A | #444441 | #2C2C2A |
| `c-blue`   | #E6F1FB | #B5D4F4 | #85B7EB | #378ADD | #185FA5 | #0C447C | #042C53 |
| `c-green`  | #EAF3DE | #C0DD97 | #97C459 | #639922 | #3B6D11 | #27500A | #173404 |
| `c-amber`  | #FAEEDA | #FAC775 | #EF9F27 | #BA7517 | #854F0B | #633806 | #412402 |
| `c-red`    | #FCEBEB | #F7C1C1 | #F09595 | #E24B4A | #A32D2D | #791F1F | #501313 |

#### Color Assignment Rules

Color encodes **meaning**, not sequence. Never cycle through colors like a rainbow.

- Group nodes by **category** — all nodes of the same type share one color.
- Use `c-gray` for neutral/structural nodes (start, end, generic steps, users).
- Use **2-3 colors per diagram**, not 6+.
- Prefer `c-purple`, `c-teal`, `c-coral`, `c-pink` for general categories.
- Reserve `c-blue`, `c-green`, `c-amber`, `c-red` for semantic meaning (info, success, warning, error).

Light/dark stop mapping (handled by the template CSS — just use the class):
- Light mode: 50 fill + 600 stroke + 800 title / 600 subtitle
- Dark mode:  800 fill + 200 stroke + 100 title / 200 subtitle

### Typography

Only two font sizes. No exceptions.

| Class | Size | Weight | Use |
|-------|------|--------|-----|
| `th`  | 14px | 500    | Node titles, region labels |
| `ts`  | 12px | 400    | Subtitles, descriptions, arrow labels |
| `t`   | 14px | 400    | General text |

- **Sentence case always.** Never Title Case, never ALL CAPS.
- Every `<text>` MUST carry a class (`t`, `ts`, or `th`). No unclassed text.
- `dominant-baseline="central"` on all text inside boxes.
- `text-anchor="middle"` for centered text in boxes.

**Width estimation (approx):**
- 14px weight 500: ~8px per character
- 12px weight 400: ~6.5px per character
- Always verify: `box_width >= (char_count × px_per_char) + 48` (24px padding each side)

### Spacing & Layout

- **ViewBox**: `viewBox="0 0 680 H"` where H = content height + 40px buffer.
- **Safe area**: x=40 to x=640, y=40 to y=(H-40).
- **Between boxes**: 60px minimum gap.
- **Inside boxes**: 24px horizontal padding, 12px vertical padding.
- **Arrowhead gap**: 10px between arrowhead and box edge.
- **Single-line box**: 44px height.
- **Two-line box**: 56px height, 18px between title and subtitle baselines.
- **Container padding**: 20px minimum inside every container.
- **Max nesting**: 2-3 levels deep. Deeper gets unreadable at 680px width.

### Stroke & Shape

- **Stroke width**: 0.5px on all node borders. Not 1px, not 2px.
- **Rect rounding**: `rx="8"` for nodes, `rx="12"` for inner containers, `rx="16"` to `rx="20"` for outer containers.
- **Connector paths**: MUST have `fill="none"`. SVG defaults to `fill: black` otherwise.

### Arrow Marker

Include this `<defs>` block at the start of **every** SVG:

```xml
<defs>
  <marker id="arrow" viewBox="0 0 10 10" refX="8" refY="5"
          markerWidth="6" markerHeight="6" orient="auto-start-reverse">
    <path d="M2 1L8 5L2 9" fill="none" stroke="context-stroke"
          stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
  </marker>
</defs>
```

Use `marker-end="url(#arrow)"` on lines. The arrowhead inherits the line color via `context-stroke`.

### CSS Classes (Provided by the Template)

The template page provides:

- Text: `.t`, `.ts`, `.th`
- Neutral: `.box`, `.arr`, `.leader`, `.node`
- Color ramps: `.c-purple`, `.c-teal`, `.c-coral`, `.c-pink`, `.c-gray`, `.c-blue`, `.c-green`, `.c-amber`, `.c-red` (all with automatic light/dark mode)

You do **not** need to redefine these — just apply them in your SVG. The template file contains the full CSS definitions.

---

## SVG Boilerplate

Every SVG inside the template page starts with this exact structure:

```xml
<svg width="100%" viewBox="0 0 680 {HEIGHT}" xmlns="http://www.w3.org/2000/svg">
  <defs>
    <marker id="arrow" viewBox="0 0 10 10" refX="8" refY="5"
            markerWidth="6" markerHeight="6" orient="auto-start-reverse">
      <path d="M2 1L8 5L2 9" fill="none" stroke="context-stroke"
            stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
    </marker>
  </defs>

  <!-- Diagram content here -->

</svg>
```

Replace `{HEIGHT}` with the actual computed height (last element bottom + 40px).

### Node Patterns

**Single-line node (44px):**
```xml
<g class="node c-blue">
  <rect x="100" y="20" width="180" height="44" rx="8" stroke-width="0.5"/>
  <text class="th" x="190" y="42" text-anchor="middle" dominant-baseline="central">Service name</text>
</g>
```

**Two-line node (56px):**
```xml
<g class="node c-teal">
  <rect x="100" y="20" width="200" height="56" rx="8" stroke-width="0.5"/>
  <text class="th" x="200" y="38" text-anchor="middle" dominant-baseline="central">Service name</text>
  <text class="ts" x="200" y="56" text-anchor="middle" dominant-b