What is Kaal Sarp Dosha?
Kaal Sarp forms when every one of the seven classical planets falls on one side of the Rahu-Ketu axis. The two shadow planets sit exactly opposite each other, and when the rest of the chart is caught between them, the life is traditionally said to move in cycles of sudden rise and sudden obstruction. Outer planets are not counted, because Jyotish does not use them.
The twelve types
The type is named from the house Rahu occupies - Anant in the 1st through Sheshnag in the 12th. Each carries a different emphasis: Anant on the self and confidence, Takshak on marriage and partnership, Sheshnag on expenditure and hidden enemies. The calculator names the type from your Rahu placement.