There are several mobile applications in the mobile application market claiming precise serve speed measurement in tennis. Most of those applications lack information regarding the validity and reliability of their measurements, thereby making them unreliable tools. A few applications, on the other hand, provide error ranges in percentages, but there is limited research validation of these percentage-based claims, with only a few videos comparing radar measurements with comparison videos presented by publishers. The primary objective of this study is to assess the validity of the most frequently used measurement tools and to investigate accuracy in quantifying serve speed through a comparative analysis with radar measurements. The sample of participants is a convenient sample consisting of male and female tennis players competing in tennis tournaments organized by the Croatian Tennis Association. Included a total of 20 individuals within the age range of 19 to 25 years. The key variables under consideration encompass the velocity of the tennis ball, as measured both by the designated application and the Stalker ATSII radar device. In the context of app-based ball speed measurement, the procedure and positioning of the measurement instrument as specified in the provided application's instructions will be followed. A designated measurer will be responsible for capturing the readings. In instances where the application facilitates the recording and review of results, the collected data will be subjected to post-measurement processing. Similarly, for radar-based ball speed measurement using the Stalker ATSII device, the prescribed settings from the instructions will be followed, and each measurement outcome will be manually documented on paper. The noteworthy aspect of these tools, offered in the form of mobile applications, resides in their affordability, widespread accessibility, and user-friendly nature. The contribution of the measuring instrument in the form of a mobile application refers to its affordability, widespread availability, and ease of use. The practical contribution of this research is evident in the use of the application as a tool for optimal planning and programming during the training process.