OLL 9
The algorithm, how to recognise it and how to practise it without cheating.
Recommended algorithm
R U R' U' R' F R2 U R' U' F'11 moves
How to recognise it
A fish: the back and left edges with the front-right corner. The front-left corner's yellow faces you.
Its inverse is another case
Do the 9 algorithm backwards, F U R U' R2 F' R U R U' R', and you are solving 13.
That's why CubeDojo never scrambles 9 that way: it builds a random state with the case fixed, so you practise 9 and not 13.
Practise 9 now
Random-state scrambles, a timer and spaced review. Free, on the web and on your phone.