Sanity is an ability score introduced in the Dungeon Master's Guide and is particularly useful for a campaign on Andrawyn. A character with high sanity remains calm and composed even in the face of the unspeakable horror of chaos creatures and corruption, while characters with low sanity are more susceptible to this horror.
Sanity checks and saving throws become necessary when a character is confronted with something that threatens his mental health and is likely to drive him insane. A messed up saving throw can therefore also result in a mental disorder whose severity and duration vary.
Sanity, however, is not an attribute in the traditional sense but is calculated from the mental ability scores intelligence, wisdom and charisma. The values of these three abilities are added together and divided by three. The result is rounded off.