Blog Chart -- Built-In SVG Data Visualization

Generates dark-mode-compatible inline SVG charts for blog posts. Invoked internally by blog-write and blog-rewrite when chart-worthy data is identified. Not a standalone user-facing command.

Styling source of truth: references/visual-media.md

Input Format

The writer or researcher passes a chart request:

Chart Request:
- Type: horizontal bar
- Title: "AI Citation Sources by Platform"
- Data: ChatGPT 43.8%, Perplexity 6.6%, Google AI Overviews 2.2%, Reddit 7.15%
- Source: Ahrefs, December 2025
- Platform: mdx (or html)

Chart Type Selection

Select based on the data pattern. Diversity is mandatory — never repeat a type within one post.

Styling Rules (Non-Negotiable)

All charts must work on both dark and light backgrounds:

Text elements:     fill="currentColor"
Grid lines:        stroke="currentColor" opacity="0.08"
Axis lines:        stroke="currentColor" opacity="0.3"
Background:        transparent (no fill on root SVG)
Subtitle text:     fill="currentColor" opacity="0.45"
Source text:        fill="currentColor" opacity="0.35"
Label text:        fill="currentColor" opacity="0.8"

Color Palette

For text inside colored elements: fill="white" with fontWeight="800".

Standard SVG Shell (HTML)

<svg
  viewBox="0 0 560 380"
  style="max-width: 100%; height: auto; font-family: 'Inter', system-ui, sans-serif"
  role="img"
  aria-label="Chart description with key data point"
>
  <title>Chart Title</title>
  <desc>Description for screen readers with all key data points and source</desc>

  <!-- Chart content -->

  <text x="280" y="372" text-anchor="middle" font-size="10" fill="currentColor" opacity="0.35">
    Source: Source Name (Year)
  </text>
</svg>

JSX/MDX Shell (camelCase attributes)

<svg
  viewBox="0 0 560 380"
  style={{maxWidth: '100%', height: 'auto', fontFamily: "'Inter', system-ui, sans-serif"}}
  role="img"
  aria-label="Chart description"
>
  <title>Chart Title</title>
  <desc>Description for screen readers</desc>

  {/* Chart content */}

  <text x="280" y="372" textAnchor="middle" fontSize="10" fill="currentColor" opacity="0.35">
    Source: Source Name (Year)
  </text>
</svg>

JSX Attribute Conversion (Required for MDX)

Chart Type Construction

Horizontal Bar Chart

Best for: percentage improvements, single-metric comparisons.

1. Define chart area: x=80, y=40, width=440, height=280
2. Calculate bar height: chartHeight / dataCount - gap (gap=8)
3. Calculate bar width: (value / maxValue) * chartWidth
4. Position bars: y = chartY + index * (barHeight + gap)
5. Label on left (right-aligned at x=75): category name
6. Value label at end of bar: percentage or number
7. Source text at bottom center

Grouped Bar Chart

Best for: before/after, A vs B comparisons.

1. Define groups along Y axis, bars within each group
2. Use 2 colors (primary + secondary) for the two series
3. Add legend at top: colored square + label for each series
4. Gap between groups > gap within groups

Donut Chart

Best for: parts of whole, market share.

1. Center: cx=280, cy=180, outer radius=140, inner radius=80
2. Calculate arc segments using cumulative angles
3. Each segment: <path d="M... A... L... A... Z" fill="color" />
4. Center text: total or key label
5. Legend below chart with color squares + labels + values

Line Chart

Best for: trends over time.

1. X axis: time periods, evenly spaced
2. Y axis: value range with 4-5 grid lines
3. Draw grid lines: stroke="currentColor" opacity="0.08"
4. Plot data points: <circle cx=... cy=... r="4" fill="color" />
5. Connect with: <polyline points="..." fill="none" stroke="color" strokeWidth="2" />
6. Optional: area fill below line with opacity="0.1"

Lollipop Chart

Best for: ranked factors, correlations.

1. Horizontal orientation (like bar chart but with circles)
2. Thin line from axis to data point: stroke="currentColor" opacity="0.15" strokeWidth="1"
3. Circle at data point: r="6" with fill color
4. Value label next to circle
5. Categories on Y axis (left-aligned)

Area Chart

Best for: distribution, cumulative data.

1. Same as line chart but with filled area below
2. Area fill: <path d="M... L... L... Z" fill="color" opacity="0.15" />
3. Line on top: stroke="color" strokeWidth="2" fill="none"
4. Grid lines behind the area

Radar Chart

Best for: multi-dimensional scoring (5-7 axes).

1. Center: cx=280, cy=190
2. Draw concentric polygons for grid (3-4 levels)
3. Calculate axis endpoints at equal angles
4. Plot data points on each axis proportional to value
5. Connect data points with filled polygon: fill="color" opacity="0.2" stroke="color"
6. Label each axis at the outer edge

Output Format

Wrap every chart in a <figure> element:

HTML:

<figure>
  <svg viewBox="0 0 560 380" style="max-width: 100%; height: auto; font-family: 'Inter', system-ui, sans-serif" role="img" aria-label="[description]">
    <title>[Chart Title]</title>
    <desc>[Full description with data points for screen readers]</desc>
    <!-- chart content -->
    <text x="280" y="372" text-anchor="middle" font-size="10" fill="currentColor" opacity="0.35">
      Source: [Source Name] ([Year])
    </text>
  </svg>
</figure>

MDX:

<figure className="chart-container" style={{margin: '2.5rem 0', textAlign: 'center', padding: '1.5rem', borderRadius: '12px'}}>
  <svg viewBox="0 0 560 380" style={{maxWidth: '100%', height: 'auto', fontFamily: "'Inter', system-ui, sans-serif"}} role="img" aria-label="[description]">
    <title>[Chart Title]</title>
    <desc>[Full description]</desc>
    {/* chart content with camelCase attributes */}
    <text x="280" y="372" textAnchor="middle" fontSize="10" fill="currentColor" opacity="0.35">
      Source: [Source Name] ([Year])
    </text>
  </svg>
</figure>

Quality Checklist (Verify Before Returning)

• No hardcoded text colors (all use currentColor)
• No white/light backgrounds (transparent or none)
• Source attribution text present at bottom
• role="img" and aria-label present on <svg>
• <title> and <desc> present inside <svg>
• Chart type not already used in this post
• If MDX: all attributes camelCased (no hyphens in attribute names)
• Data values match the source data exactly
• Color palette uses only approved colors
• ViewBox is 0 0 560 380 (standard) or justified alternative