Analysing the performance of OWL reasoners on expressive OWL ontologies is an ongoing challenge. In this paper, we present a new approach to performance analysis based on justifications for entailments of OWL ontologies. Justifications are minimal subsets of an ontology that are sufficient for an entailment to hold, and are commonly used to debug OWL ontologies. In JustBench, justifications form the key unit of test, which means that individual justifications are tested for correctness and reasoner performance instead of entire ontologies or random subsets. Justifications are generally small and relatively easy to analyse, which makes them very suitable for transparent analytic micro-benchmarks. Furthermore, the JustBench approach also allows us to isolate reasoner errors and inconsistent behaviour. We present the results of initial experiments using JustBench with FaCT++, HermiT, and Pellet. Finally, we show how JustBench can be used by reasoner developers and ontology engineers seeki...