After specifying targets and feedstocks, the number of steps to be searched backwards (up to 15) should be provided. Many heuristics have been devised to guide the search and to filter results, Table . Most are lumped in "Advanced Settings" with default configurations. New users may get better understanding of how to curate "Advanced Settings" after the first round of search. Preference of molecular fragments and yield threshold of reactions are picked in the first round of search, since fragment-based heuristic may be relevant to many search objectives, see Fig. .