Why this exists

Every opening resource teaches you the main line. Almost none of them prepare you for the fact that, below 1800, your opponent leaves it on move four or five, usually with a move that is objectively bad.

Knowing the theory does not help there. Knowing what to do the moment they leave it does. So this trains three separate things instead of pretending they are one: knowing the line, exploiting the moment someone leaves it, and remembering both of them a month later.

Where the puzzles come from

They are not written. For every position in the courses we look at what players in your rating band really play there, keep the moves that are frequent and refutable, and verify each refutation with an engine. Any position where more than one move works is discarded, because a puzzle with several right answers is a frustrating puzzle. The result is a set of mistakes that will genuinely be played against you.

Who makes it

A small independent studio that also builds ChessEndings and DarkSquares. The opening content is written by a titled player.