Karaten

Example of a karaten riichi, with all waiting tiles circled in red.

Karaten 「カラテン」, or empty tenpai, is a state where a tenpai hand does not have the ability to win. This is due to unavailability of all instances of winning tiles. The "visible tiles" may either be discarded, used as a dora indicator, or already exist in one's hand. Furthermore, they may be held in other player's hands or even reside within the dead wall. However, the latter case is beyond a player's visibility.

Ambiguity

Karaten tenpai acquired after calling kan.

The term is often confused with the "fifth tile" case. Here, a hand waiting for a fourth tile that is simply hidden, discarded, or used by someone else remains a valid tenpai in all circumstances. A hand may contain a 1-2 penchan and a previously declared kan of 3-3-3-3 in the same suit. This renders the threes unavailable as winning tiles. It would be announced what qualifies as tenpai or not. As a precaution, it is almost always mentioned.

Example:
Waiting for:

Quirks

• On Ron2, there has been an instance of a person being able to call riichi with a gutshot wait shape for a 6-pin when they have made a closed kan of 6-pin already. The hand was considered noten, but did not trigger a chombo penalty (mainly due to programming assuming no one could do something that could be viewed as faulty). The hand was not in a valid tenpai shape when it came to scoring a drawn hand, but not okay for determining if a player was legally allowed to declare riichi.
• On Tenhou, there have been reports of a hand containing 12s44466688p with a kan of 3s, scored as in tenpai. Likewise, the same kind of case is allowable in Mahjong Soul.