Chart Builder Skill

Dark-themed, accessible data visualization generator.

When to Trigger

Activate this skill when the user:

• Asks to create a chart, graph, or data visualization
• Wants to visualize data from an API, database, or static dataset
• Requests a dashboard component with charts
• Needs to display metrics, trends, or comparisons visually

Stack Selection

| Scenario | Library | Reason | |----------|---------|--------| | Standalone chart, no React | Chart.js | Lightweight, canvas-based | | React/Next.js project | Recharts | Native React components, composable | | Complex interactive dashboards | Recharts | Better state management integration | | Static image export needed | Chart.js | Canvas toDataURL() support |

Design System

All charts must follow these design tokens to match the user's dark theme:

Colors

js
const chartTheme = {
  background: '#18181B',        // zinc-900
  surface: 'rgba(255,255,255,0.05)',  // glass bg
  border: 'rgba(255,255,255,0.10)',   // glass border
  gridLines: 'rgba(255,255,255,0.06)',
  labelText: '#D4D4D8',        // zinc-300
  valueText: '#F4F4F5',        // zinc-100
  tooltip: {
    bg: 'rgba(24,24,27,0.90)',
    border: 'rgba(255,255,255,0.10)',
    blur: '16px',
  },
};

Accent Palette

Use these for data series — ordered by visual priority:

| Index | Name | Hex | Use case | |-------|------|-----|----------| | 0 | Blue | #3B82F6 | Primary metric | | 1 | Purple | #8B5CF6 | Secondary metric | | 2 | Emerald | #10B981 | Positive/growth | | 3 | Amber | #F59E0B | Warning/attention | | 4 | Rose | #F43F5E | Negative/decline | | 5 | Cyan | #06B6D4 | Tertiary metric |

Glass Morphism Container

Wrap every chart in a glass container:

jsx
<div className="backdrop-blur-xl bg-white/5 border border-white/10 rounded-2xl p-6">
  <h3 className="text-zinc-100 text-lg font-semibold mb-4">{title}</h3>
  <div className="min-h-[300px]" role="img" aria-label={ariaLabel}>
    {/* Chart component */}
  </div>
</div>

Chart Types

Line Chart

Best for: trends over time, continuous data.

• Use gradient fill below the line (linearGradient from accent to transparent)
• Smooth curves: type="monotone" (Recharts) or tension: 0.4 (Chart.js)
• Show data points on hover only (reduce visual clutter)

Bar Chart

Best for: comparisons between categories.

• Rounded top corners: radius={[4, 4, 0, 0]}
• Max bar width: 48px (prevent oversized bars on few data points)
• Add value labels above bars for small datasets (under 8 items)

Area Chart

Best for: volume/magnitude over time.

• Stack multiple areas for composition views
• Use decreasing opacity for stacked layers (0.6, 0.4, 0.2)
• Gradient fill from accent color to transparent

Pie / Donut Chart

Best for: part-to-whole relationships (max 6 segments).

• Donut preferred over pie (inner radius 60%)
• Active segment: slight outward offset on hover
• Center label: total value or primary metric
• Legend positioned below on mobile, right on desktop

Scatter Chart

Best for: correlation between two variables.

• Variable dot size for third dimension (bubble chart)
• Add quadrant lines if meaningful thresholds exist
• Tooltip shows both axis values plus label

Radar Chart

Best for: multi-dimensional comparison (3-8 axes).

• Filled area with low opacity (0.2)
• Grid lines match the dark theme
• Limit to 2-3 overlapping datasets for readability

Accessibility Requirements

Every chart must include:

1. ARIA attributes:

jsx <div role="img" aria-label="Monthly revenue trend showing 23% growth from January to June 2025">

1. Reduced motion:

css @media (prefers-reduced-motion: reduce) { .chart-container * { animation: none !important; transition: none !important; } }

1. Color independence: Never rely on color alone to convey meaning. Add:

• Pattern fills or dash styles for line differentiation
• Direct labels or legends with text descriptions
• Shape variation for scatter plots

1. Screen reader fallback: Include a hidden data table:

jsx <table className="sr-only"> <caption>Monthly revenue data</caption> {/* Full data in tabular form */} </table>

1. Contrast: All text on the chart must meet WCAG AA (4.5:1 ratio against zinc-900).

Responsive Behavior

• Charts fill their container width (responsive: true / width="100%")
• Set min-h-[300px] on the wrapper to prevent CLS
• On mobile (< 640px): move legends below the chart, reduce font sizes
• On print: switch to light theme with black text (via @media print)

Performance

Charts are heavy — always lazy load:

jsx
import dynamic from 'next/dynamic';

const RevenueChart = dynamic(() => import('@/components/charts/RevenueChart'), {
  loading: () => (
    <div className="backdrop-blur-xl bg-white/5 border border-white/10 rounded-2xl p-6 min-h-[300px] animate-pulse" />
  ),
  ssr: false,
});

• Never put chart components in the LCP critical path
• Use ssr: false — canvas/SVG charts need the DOM
• Skeleton matches the glass container dimensions exactly

Tooltip Styling

jsx
const CustomTooltip = ({ active, payload, label }) => {
  if (!active || !payload) return null;
  return (
    <div className="backdrop-blur-xl bg-zinc-900/90 border border-white/10 rounded-lg px-3 py-2 shadow-xl">
      <p className="text-zinc-400 text-xs mb-1">{label}</p>
      {payload.map((entry, i) => (
        <p key={i} className="text-zinc-100 text-sm font-medium">
          <span style={{ color: entry.color }}>●</span> {entry.name}: {entry.value}
        </p>
      ))}
    </div>
  );
};