OLL 38
The algorithm, how to recognise it and how to practise it without cheating.
Recommended algorithm
R U R' U R U' R' U' R' F R F'12 moves
How to recognise it
A W, like stairs: front-left corner, left edge, back edge and back-right corner. The front-right corner's yellow faces right.
Its inverse is another case
Do the 38 algorithm backwards, F R' F' R U R U R' U' R U' R', and you are solving 31.
That's why CubeDojo never scrambles 38 that way: it builds a random state with the case fixed, so you practise 38 and not 31.
Practise 38 now
Random-state scrambles, a timer and spaced review. Free, on the web and on your phone.