API Sanity Checker (ASC) is an automatic generator of basic unit tests for shared C/C++ libraries. It is able to generate reasonable (in most, but unfortunately not all, cases) input data for parameters and compose simple ("sanity" or "shallow"-quality) test cases for every function in the API through the analysis of declarations in header files. The quality of generated tests allows to check absence of critical errors in simple use cases. The tool is able to build and execute generated tests and detect crashes (segfaults), aborts, all kinds of emitted signals, non-zero program return code and program hanging. It may be considered as a tool for out-of-the-box low-cost sanity checking (fuzzing) of the library API or as a test development framework for initial generation of templates for advanced tests. Also it supports universal format of tests, random test generation mode, specialized data types and other useful features.