WWYC (“What Would You Cut”, or “nani kiru”), are problems where you have to choose the correct discard in the situation you are given. The process of figuring out the answer – and the reason why – can quickly improve your game.

A link to a nanikiru program is incoming once it is done, but for now, here’s a couple, from Healthy Mahjong (thanks to Vysaga for the translations):

East 1, Player North, 5th go-around, Score +/- 0 from 1st
Dora Indicators:

Draw:

You’ve got a leftover , but when it comes to picking one, WWYC?

Answer:
8s. Of the three, the 8p and 8s connect with the least possible tiles – a 6/7/8/9, as opposed to the 5s 3/4s/5s/6s/7s. the 8s, however, overlaps waits with the 5s – both are waiting on a 6s/7s, so cutting the 8s loses you less waits (just the 8s/9s) than the 8p.

East 4, Player West, 5th go-around, Score – 3700 from 1st
Dora Indicators:

Draw: ]

You’ve got a pair of dora, which with Reach is enough to get the lead. so you want to get to tenpai as fast as possible. WWYC?

Answer:
7p. You would then be waiting on 1m/4m/5p/8p/9p/2s, most of which are open waits, and an 8p gives you Ii Pei Ko. You could think about cutting the 9p, but then you have one less wait (a single 7p), and no Ii Pei Ko chance.