You can use the standard tooltip which is enabled by default (ShowToolTip = true) or enable an event bubble (an extended tooltip).
The default tooltip text is set to the event text and you can customize it in BeforeEventRender event handler.
ASP.NET WebForms
protected void DayPilotCalendar1_BeforeEventRender(object sender, BeforeEventRenderEventArgs e) { e.ToolTip = "my tooltip"; }
ASP.NET MVC
protected override void OnBeforeEventRender(BeforeEventRenderArgs e) { e.ToolTip = "my tooltip"; }
JavaScript
<div id="dp"></div> <script type="text/javascript"> var dp = new DayPilot.Calendar("dp"); dp.events.list = [ { start: "2013-03-25T00:00:00", end: "2013-03-25T12:00:00", id: "123", text: "Event", toolTip: "my tooltip" } ] // ... dp.init(); </script>