A more thorough explanation:

The simple-tool rule is a principle that states that an employer is not responsible for warning their employees about obvious dangers. Additionally, the employer is not required to inspect a tool that is under the complete control of an employee who is fully aware of the tool's condition.

For example, if an employee is using a hammer to drive a nail into a piece of wood, the employer does not need to warn the employee about the potential danger of hitting their finger with the hammer. This danger is obvious to anyone who has used a hammer before. Similarly, if the employee is using a saw that they have used many times before and are familiar with its condition, the employer does not need to inspect the saw.

Another example could be a construction worker who is using a ladder to reach a high place. If the ladder is in good condition and the worker has used it before, the employer does not need to inspect the ladder or warn the worker about the potential danger of falling.

The simple-tool rule is based on the assumption that employees are responsible for their own safety when using tools that they are familiar with. Employers are only responsible for providing safe tools and equipment and ensuring that employees are properly trained to use them.