Security Information and Event Management tools, log management tools, log analysis tools, and other event data management tools are enhanced. Enhancements harvest entity extraction rules from queries, query results, and other examples involving the extraction of field values from large amounts of data, and help perform entity extraction efficiently. Entity extraction operations locate IP addresses, usernames, and other field values that are embedded in logs or data streams, for example, and populate object properties with extracted values. Previously used extraction rules are applied in new contexts with different users, different data sources, or both. An entity extraction rules database serves as a model that contains rules specifying parsing mechanisms. Parsing mechanisms may include regular expressions, separation character definitions, and may process particular file formats or object notation formats or markup language formats. A recommender suggests extraction rules to users, based on frequency, machine learning classifications, correctness certainty, or other considerations.