The phrase "according to rule" can be replaced with several synonyms based on its meaning and usage. Some commonly used synonyms include "by the book," "in compliance with regulations," "following protocols," "in accordance with standards," "by the law," and "in conformity with policy." Each of these synonyms conveys the idea that something is done in conformity with established guidelines or principles. These synonyms are useful when describing actions that adhere to a set of rules or laws that are intended to govern a particular situation. In essence, they highlight the importance of following established protocols to ensure that things are done correctly and effectively.