Building static analyzers for modern programming languages is difficult. Often soundness is a requirement, perhaps with some well-defined exceptions, and precision must be adequate for producing useful results on realistic input programs. Formally proving such properties of a complex static analysis implementation is rarely an option in practice, which raises the challenge of how to identify causes and importance of soundness and precision problems.

Through a series of examples, we present our experience with semi-automated methods based on delta debugging and dynamic analysis for increasing soundness and precision of a static analyzer for JavaScript. The individual methods are well known, but to our knowledge rarely used systematically and in combination.