Calendar heatmap

Skill shuakami/paperchart/skills/calendar-heatmap

Quiet, editorial chart PNGs for technical blog posts. 15 primitives, six themes, one CLI.

Install

npx -y skills add shuakami/paperchart --skill calendar-heatmap

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What its author says it does

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Render a GitHub-style calendar heatmap. A grid with 7 rows (weekdays) and 53 columns (ISO weeks). Each cell is one day, shaded by `value` using four-bucket opacity steps of the accent colour. Use for daily-activity grids, deployment-frequency maps, error-incidence calendars.

The file declares its own license as MIT. That is the author’s claim about this one file, and it is not the same thing as the license GitHub reports for the repository, which is listed with the other numbers below.

SKILL.md

1.6 KB, as published. Nobody here has run it

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