Fuzzing is a software testing method that involves passing malformed data as input to the program and monitoring it for misbehavior. Today, fuzzing is one of the most effective ways to find software security problems. In 2014, Michał Zalewski presented American Fuzzy Lop, the first coverage guided fuzzer. This started the modern world of fuzzing solutions and techniques on the market. In this article, we will discuss libFuzzer, a LLVM utility that allows you to integrate fuzzing methodology into your libraries, and briefly introduce techniques to maximize the effectiveness of catching problems.