The Keys are extremely powerful sorcerous objects, possibly possessing the power of the Architect Herself. The Keys hold different amounts of power, although the Seventh Key is dominant. Also, the Keys are only at full power in their former master's domain in the House, and only during their former master's namesake day in the Secondary Realms. The powers of the Keys are very numerous, so not all powers are known. They have been known to leave residues of sorcerous power after use and a little of the power remains even when the key has been given away. If the person is tainted enough with sorcery, they will become a denizen, unable to return to the mortal realms.
The Keys, once claimed by the Rightful Heir, must be given willingly for anyone else to wield their power. Arthur gives them to Dame Primus to use as his steward, and she is the only one other than Arthur and the Trustees to be seen using the Keys throughout the series. However, this permission must be willing: when Lord Sunday chains Arthur to a clockface and threatens to have his eyes poked out (much like the Old One) until Arthur relinquishes the Keys, he does not go through with his threat. Arthur deduces that this is because permission gained through torture is not truly willing, and therefore would not work.
- Main article: First Key
The First Key, formerly held by Mister Monday, took the shape of a minute hand and an hour hand, which could be joined together to form a sword in the shape of a clock hand. The First Key's powers, as described by the Old One, are to "lock, unlock, bind, unbind, open, close, animate, petrify, illuminate, darken, translate, befuddle, and to perform small diversions or redirections of Time." It has been observed to be able to freeze and encase objects within ice, kill, heal, and in general, manipulate anything in the surrounding environment. The Hour Hand is stronger but the Minute Hand is faster and can be used more frequently.
- Main article: Second Key
The Second Key, formerly held by Grim Tuesday, took the shape of silver gauntlets with the power to create or alter things made from Nothing, grant the owner telekinetic powers and create a protective shield around the wearer. These gloves were used during a competition between Tuesday and Arthur over who would get the key, which was judged by the Mariner.
- Main article: Third Key
The Third Key, formerly held by Drowned Wednesday, took the shape of a trident with the power to change the size of itself and the user. It was used by Wednesday in a attempt to keep herself from growing any larger as a Leviathan. She could also use it to change back into human form for a limited time. It can stop people from sinking and can control the liquids in people's bodies.
- Main article: Fourth Key
The Fourth Key, formerly held by Sir Thursday, took the shape of a baton, as the user wished, and could impose obedience on its target. When in danger the baton took the shape of a broad sword for Sir Thursday and a rapier for Arthur. It can magnify a persons voice and make them a better fighter.
- Main article: Fifth Key
The Fifth Key, formerly held by Lady Friday, took the shape of a small hand mirror. It held the power to transport the holder though any reflective surface to a place the holder has been before. It could also drain the emotions from Mortals. It had the ability to shoot a beam of heat that could disintegrate an object.
- Main article: Sixth Key
The Sixth Key, formerly held by Superior Saturday, took the shape of a quill pen. While not much is known of the Sixth Key, it is assumed that whatever is written with the Sixth Key shall come into being. (ie. writing pierce and having the word pierce the target.) As is learned in Superior Saturday, it could also write spells like other quills in the Upper House although they had enhanced power.
- Main article: Seventh Key
The Seventh Key, formerly held by Lord Sunday, took the shape of a tiny key, about as small as someone's little finger. It is the most powerful Keys and Lord Sunday was able to use it to help restrain the fifth and sixth Keys combined. He has also shown to use the Keys to silence Arthur and call down lightning that could kill several of the Mariner's sailors. It is the last Key that Arthur claims and and joins the fifth Key on a chain around his neck when he becomes the New Architect.