In the first analysis, we assessed if synthetic accessibility scores can model and predict outcomes of retrosynthesis planning. To express the complexity of retrosynthesis planning, we analyzed the search trees of AiZynthFinder runtime for molecules from our database. For these trees, we calculated statistics, such as the number of nodes, treewidth, and the number of leaf nodes that are not omitted analyze tree depth because AiZynthFinder has strict limits for the depth of the search tree and the results would be uninformative. Moreover, we checked if synthetic accessibility scores can act as nodes' prioritization heuristics. To this end, we classified all nodes into three groups: solved, not solved, and internal (cf. Figure ). Solved nodes correspond to complete solutions, i. e. all their molecules are available in stock. Not solved nodes correspond to partial solutions of an infeasible synthetic route. We define not solved nodes as nodes for which there is no path leading to a solved node. The rest of the nodes are internal, i.e. nodes having a path to the solved leaf node. They correspond to these partial solutions which eventually lead to a complete solution. For such nodes definition, if the root of a tree is not solved then the algorithm has not found any feasible synthetic route for a given target molecule. We express a score value of a node as one of the statistics (maximum, minimum, arithmetic mean) over all molecules in the node. For making calculations comparable, all scores were transformed so that they achieve values from the range [0, 1] with 0 corresponding to an infeasible (non-synthesizable) molecule and 1 corresponding to a feasible (easily synthesizable) molecule. To check if synthetic accessibility scores properly prioritize nodes, we analyzed if synthetic accessibility scores discriminate internal nodes from not solved ones. Firstly, we considered these pairs connected with a single reaction step. We analyzed two configurations: i) siblings nodes internal and not solved with common internal parent and ii) internal parent from not solved child (cf. Figure ). Secondly, we synthetic accessibility scores correctly discriminate internal nodes from not solved ones in general. Finally, we checked if modified leaf selection, which incorporates nodes' synthetic accessibility scores, may speed up retrosynthesis planning. To this point, we modified UCB (Equation ( )) by substituting fraction of a reward with one of the synthetic accessibility scores. Specifically, a reward (Equation ( )) was replaced with the value: