OLL 13
The algorithm, how to recognise it and how to practise it without cheating.
Recommended algorithm
F U R U' R2 F' R U R U' R'11 moves
Alternatives
r U' r' U' r U r' F' U F10 moves
How to recognise it
A line through the left and right edges, plus the front-left corner. The front-right corner's yellow faces you.
Its inverse is another case
Do the 13 algorithm backwards, R U R' U' R' F R2 U R' U' F', and you are solving 9.
That's why CubeDojo never scrambles 13 that way: it builds a random state with the case fixed, so you practise 13 and not 9.
Practise 13 now
Random-state scrambles, a timer and spaced review. Free, on the web and on your phone.