LibFuzzer, a coverage-guided evolutionary fuzzing tool, is a fuzzing engine that works in the background. LibFuzzer links with the library being tested and feeds fuzzed data to the library through a specific fuzzing target function. The fuzzer tracks the code coverage and generates mutations based on the input data to maximize it. SanitizerCoverage, an instrumentation of LLVM, provides code coverage information. LibFuzzer will still be fully supported, in that important bugs are fixed. To use libFuzzer with a library, you must first implement a fuzz-target. This is a function which accepts an array and performs something interesting using the API being tested. This fuzz target is not dependent on libFuzzer, so it can be used with other fuzzing engine like AFL or Radamsa.