# Welcome to the Highcharts Gantt JS (gantt) Options Reference

These pages outline the chart configuration options, and the methods and properties of Highcharts objects.

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# plotOptions.series.tooltip.headerFormat

The HTML of the tooltip header line. The context is the Point class. Variables are enclosed in curly brackets. Examples of common variables to include are `x`, `y`, `series.name` and `series.color` and other properties on the same form. The `point.key` variable contains the category name, x value or datetime string depending on the type of axis. For datetime axes, the `point.key` date format can be set using `tooltip.xDateFormat`. In v12+, locale-aware date names follow the browser's casing and can be lower-case, so use the `ucfirst` helper (for example `{ucfirst point.key}`) if you want a capitalized header.