ChemBalancer attempted to complete the reaction structures from the available resources (the candidate reagents and solvents, and the help species) by a heuristic approach. All reaction records from Reaxys ® and USPTO databases were passed to ChemBalancer, with their completion results shown in Table . In USPTO and Reaxys ® , 17.6% and 44.1% of reaction records were complete with ChemBalancer respectively. These complete reactions include the originally complete reactions, reaction completed by adding candidate reagents to the LHS (or, reagents to the LHS and help species to the RHS), and reaction completed by adding help species to the RHS. It is noticed that ChemBalancer has better performance on Reaxys ® reactions over USPTO. A very high percentage of reactions in USPTO remains incomplete due to their RHS species insufficiency. This means that most reactions could not identify their side products from the library of help species. A larger set of help species was attempted to have more diverse solutions to complete the reactions. This list included 3,526 frequently appearing small species. However, from a set of LHS atom surplus reactions, enlarging the library of help species from 32 to 3,526 frequently appeared molecules as reaction side products was also attempted. However, this could only improve the reaction completion rate by 0.3%, but significantly increased computational time for the enumeration. This suggests that current 32 help species are sufficient to comprise the help species library. This also indicates a case-specific heuristic method, or a predictive machine learning is preferred to predict the exact side products for the RHS insufficient reactions. It is also noticed that the ratio of reactions with RHS species insufficiency is much higher in the USPTO reactions. This might be because the USPTO reaction extraction algorithm incorrectly added reagents into the reaction SMILES as reactants. Using the atom mapping tool RXNMapper, it is noticed that the reactants from a great number of USPTO reactions have no atom mapped into the reaction products. With no contribution to the carbon flow, these reactant molecules were supposed to be added into the reagent categories. Adding these into reactants would cause LHS atom surplus, and therefore result in RHS species insufficiency. The USPTO complete reaction ratio would be higher if these false labelled reactants could be removed.