Fairly well, but they could do better. Static analysis tools such as FindBugs tend to flag problems which are easy to diagnose. While many coding rules are easy to diagnose automatically, some are quite difficult or impossible. For instance, determining if a Java object variable might be null can require in-depth whole program analysis, and a perfect analysis is not technically feasible now. (and probably will never be). Some tools instead use heuristics (eg if we check that this variable is null 5 times out of 6, than that 6th one is probably an error).