Abstract: A system assigns target systems to users for identifying system defects. The system ranks the users using a machine learning model. The system extracts a feature vector describing a target system. The system extracts features describing each user. The system provides the features describing the user and the features describing the target system as input to a machine learning model. The machine learning model is trained to receive information describing an input user and an input target system and predict a score indicating a likelihood of the input user providing a system defect in the input target system. The system executes the machine learning model to predict a score for each user. The system ranks the users based on the scores. The system ranks the users based on the scores and communicates with a subset of users selected based on the ranking.