According to the WSJ, the Excel-based application designed to decode opposing catchers' signs was used throughout the 2017 season and for part of 2018 by Astros baseball operations employees and video room staffers both at home and on the road.
Staffers would log the catcher's signs and subsequent pitches into a spreadsheet and "Codebreaker" would determine how the signs related to different pitches. The information would then be communicated to the hitter by a baserunner via an intermediary.


Astros players eventually evolved the system to include banging on a trash can to warn hitters of the coming pitch.
Ex-Astros general manager Jeff Luhnow told MLB investigators that he remembers the intern's PowerPoint slide about "Codebreaker," but said he thought it would be used to legally decipher signs from previous games, according to the WSJ.

Luhnow was fired by the Astros last month, shortly after MLB suspended him for one season.