The Marauder’s Map is a magical document that reveals all of Hogwarts School of Witchcraft and Wizardry. Not only does it show every classroom, every hallway, and every corner of the castle, but it also shows every inch of the grounds, as well as all the secret passages that are hidden within its walls and the location of every person in the grounds, portrayed by a dot. It is also capable of accurately identifying each person, and is not fooled by animagi, polyjuice potions, or invisibility cloaks; even the Hogwarts ghosts are not exempted from this. It can also reveal secret passages the Marauders found, though it only did this on one known occasion.
The map is normally disguised as a blank piece of parchment. To view the map, one must tap it with one’s wand and recite, “I solemnly swear that I am up to no good.” The content of the map will reveal itself.
To hide the contents of the map so the parchment appears blank again, one must again tap it and recite, “Mischief managed.”