Self-contained, plain Go implementation of calendar heatmap inspired by Github contribution activity.

$ go build
$ echo '{
    "2020-05-16": 8,
    "2020-05-17": 13,
    "2020-05-18": 5,
    "2020-05-19": 8,
    "2020-05-20": 5
}' | ./calendarheatmap > chart.png

• Basic

• Negative values presented via an alternative color scheme

• Colorscales

• UTF-8

• SVG

• Without month separator

• Without labels

• Without labels, without separator

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