ABI Compliance Checker (ACC) is a tool for checking backward binary and source-level compatibility of a C/C++ library. The tool checks header files and shared libraries of old and new versions and analyzes changes in API and ABI (ABI=API+compiler ABI) that may break binary and/or source compatibility: changes in calling stack, v-table changes, removed symbols, renamed fields, etc. Binary incompatibility may result in crashing or incorrect behavior of applications built with an old version of a library if they run on a new one. Source incompatibility may result in recompilation errors with a new library version. The tool is intended for developers of software libraries and maintainers of operating systems who are interested in ensuring backward compatibility, i.e. allow old applications to run or to be recompiled with newer library versions.