In this paper, we describe FindBugs, an open source static analysis tool for Java, and experience using it in production settings. FindBugs does not push the envelope in terms of the sophistication of its analysis techniques. Rather, it is designed to evaluate what kinds of defects can be effectively detected with relatively simple techniques and to help us understand how such tools can be incorporated into the software development process. FindBugs has become very popular, downloaded more than 500,000 times and used by many major companies and software projects. We report on experience running FindBugs against Sun’s JDK implementation, using Findbugs at Google where it has been used for more than a year and a half and incorporated into their standard development process, and preliminary results from a survey of FindBugs users.