Free local tool

Calendar Heatmap Maker

Turn ISO date and nonnegative value rows into a local full-year calendar intensity heatmap.

Private by design: inputs and local files stay in this browser tab. The tool sends no input to a server and stores nothing after the page closes.

JavaScript is required for the interactive tool.

Method and limits

Renders every date in one selected year, including leap day, with Sunday or Monday week starts. Duplicate dates are summed. Zero stays empty; positive values use four linear levels relative to the year maximum. Time zones are not applied to ISO date-only input.