Filleted end milling is commonly used as a versatile manufacturing process, whereas the optimization for tool condition management is one of the continuously noticed topics. It can also contribute to the achievement of Sustainable Development Goals. A lot of outcomes have been reported so far in the experimental investigations of tool condition parameters. However, the findings and knowledge from theoretical perspective are relatively scarce to advance smart tool management. Hence, the aim of this study is to give theoretical consideration with tool condition parameters. The investigations focus on filleted end milling with some variations of machining conditions. Several tool condition parameters were theoretically proposed after illustrating geometrical modeling with variable description. Then, the demonstrations and discussion were made based on the computational results in filleted end milling. The results visually and numerically ascertained novel findings regarding several characteristics of tool condition parameters.