HEALERS is a practical, high-performance toolkit that can enhance the robustness and security of existing applications. For any shared library, it can find all functions defined in that library and automatically derives properties for those functions. Through automated fault-injection experiments, it can detect arguments that cause the library to crash and derive safe argument types for each function. The toolkit can prevent heap and stack buffer overflows that are a common cause of security breaches. The nice feature of the HEALERS approach is that it can protect existing applications without access to the source code.