Paperchart Calendar Heatmap

paperchart — calendar heatmap

52-53 columns × 7 rows. Columns are ISO weeks, rows are weekdays (Sun-Sat). Each square is one day, shaded by value using four-bucket opacity steps. Month labels sit above the grid; a small less … more legend sits at the bottom right.

When to use

• Contribution / commit activity over a year.
• Deployment frequency or incident calendar.
• Any daily-count dataset spanning roughly one year.

Input shape

{
  "data": {
    "start": "2025-06-01",
    "buckets": 4,
    "days": [
      { "date": "2025-06-01", "value": 0 },
      { "date": "2025-06-02", "value": 3 },
      { "date": "2025-06-03", "value": 7 }
    ]
  }
}

Or just an array of { date, value }:

{ "data": [{ "date": "2025-06-01", "value": 0 }, { "date": "2025-06-02", "value": 3 }] }

Visual rules

• Missing dates render as empty (zero-value) cells.
• Accent is applied to the highest bucket; lower buckets use tinted versions of the same hue.
• Month labels only above the first column of each month.

CLI

paperchart calendar-heatmap -i data.json -o cal.png
paperchart calendar-heatmap --defaults -o cal.png