Fundamental movement skills (FMS), considered as building blocks of movement, have received growing interest due to their significant impact on both present and future health. FMS are categorized into locomotor, object control and stability skills. While there has been extensive research on assessing the proficiency and reliability of locomotor and object control skills, stability skills have received comparatively less attention. For this reason, this study aimed to assess the test–retest, intrarater and interrater reliability of five stability skills included in the Alfamov app. The performance of eighty-four healthy primary school children (60.8% girls), aged 6 to 12 years (mean ± standard deviation of 8.7 ± 1.8 years), in five stability skills was evaluated and scored by four raters, including two experts and two novices. The Alfamov tool, integrating various process-oriented tests, was used for the assessment. Reliability analyses were conducted through the computation of the intraclass correlation coefficient (ICC) along with the corresponding 95% confidence intervals. Good-to-excellent intrarater reliability, excellent interrater reliability and moderate-to-good reliability in the test–retest were achieved. The results proved that Alfamov is a robust test for evaluating stability skills and can be suitable for use by different professionals with less experience in assessing children’s motor competence.