Chart Skill

A table of numbers hides the story; a chart shows it. This skill turns data into a clean, correctly-typed chart — a trend as a line, a comparison as bars, a composition as a pie/doughnut — emitted as a small JSON spec inside a ```chart block that renders live in the playground (and exports as PNG).

Required Inputs

Ask for these only if they aren't already provided:

• The data — the numbers, with their labels/categories (paste a table, list, or metrics).
• What you want to show — a trend over time, a comparison between things, or parts of a whole. This decides the chart type.
• Series — one metric or several (e.g. revenue and churn over the same months).
• Title (optional) — what the chart is about.

If the data implies the wrong chart type for the goal, pick the right type and say why.

Output Format

[What the chart shows]

A one-line read — the takeaway the chart makes obvious.

{
  "type": "line",
  "title": "MRR vs. churned MRR (2026)",
  "labels": ["Jan", "Feb", "Mar", "Apr", "May", "Jun"],
  "series": [
    { "name": "MRR ($k)", "data": [120, 138, 151, 167, 180, 201] },
    { "name": "Churned ($k)", "data": [8, 9, 7, 11, 9, 8] }
  ]
}

Notes (optional) — caveats, the source of the numbers, or what a follow-up chart would show.

Chart Spec Rules (so it renders)

• Emit a single ```chart block containing valid JSON (double-quoted keys/strings, no trailing commas, no comments).
• type: "bar", "line", "area", "pie", or "doughnut".
• labels: the x-axis categories (or the slice names for pie/doughnut).
• series: an array of { "name": "...", "data": [numbers] }. Pie/doughnut uses the first series only.
• Every series' data length must match labels length. Numbers only — no units inside the array (put units in the series name or title).
• Choose the type by intent: trend over time → line/area; compare categories → bar; parts of a whole → pie/doughnut.

Quality Checks

• Chart type matches the intent (trend → line, comparison → bar, composition → pie)
• The JSON is valid and renders without edits (no trailing commas, all strings quoted)
• Every series' data length equals the number of labels
• Units/scale are clear (in the title or series names), and the one-line read states the takeaway
• Multiple series are used only when they share the same axis/scale

Anti-Patterns

• Do not use a pie chart for more than ~6 slices or for trends — pies show composition, not change
• Do not put units or text inside the numeric data array — it breaks the chart
• Do not emit invalid JSON (trailing commas, single quotes, comments) — it won't render
• Do not mismatch lengths — a series shorter/longer than the labels misaligns the chart
• Do not chart numbers you weren't given — flag gaps instead of inventing data points

Based On

Data-visualization practice (chart-type-to-intent: trend/comparison/composition), emitted as a renderable chart spec.