Today’s complex software-based safety critical systems depend on software tools for automation and efficiency. “Tool qualification” is a generic term to describe a process designed to ensure that the risk of a tool error impacting the safety of a system is acceptably low – either because the errors are few, or because they cannot impact safety. Most functional safety standards define processes to achieve tool qualification by considering the application of the tool, and the environment in which it is deployed. The application considerations are designed to ensure that the tool is used in such a way that potential errors are either avoided or detected. The environmental perspective looks to ensure that the installed tool works as part of the broader tool chain to which it contributes, building confidence and trust in the tool and its use. All standards have a classification phase to establish the required confidence in the tool and a qualification phase that provides this level of confidence for some or all of its functionality. However, the classification and qualification methods differ in some details.