This study aims to develop a self-assessment tool to help university students independently evaluate their digital and online competencies (DOCs). A quantitative methodology was employed, focusing on instrument validation and its ability to measure DOCs effectively. The development process was conducted in four structured phases, combining theoretical foundations with empirical testing. Data were collected from 945 students in the initial survey to test the instrument’s reliability and validity, followed by a larger sample of 2954 students for confirmatory analysis using Structural Equation Modelling–Partial Least Squares (SEM-PLS). The results confirmed that the tool provides a robust, scientific scale capable of measuring DOCs accurately. Additionally, this tool allows students to assess their readiness and improve their competencies in alignment with the increasing demands of digital learning environments in higher education. The research highlights the importance of developing scalable, adaptable self-assessment instruments to support lifelong learning and digital literacy among students. This validated scale offers significant potential for broader implementation and research in educational technology contexts.