Nowadays, usability can be meant as an important quality characteristic to be considered throughout the software development process. A great variety of usability techniques have been proposed so far, mostly intended to be applied during analysis, design and final testing phases in software projects. However, little or no attention has been paid to the analysis and measurement of usability in the implementation phase. Most of the time, usability testing is traditionally executed in advanced stages. However, the detection of usability flaws during the implementation is of utmost importance to foresee and prevent problems in the utilization of the software and avoid significant cost increases. In this paper, we propose a feasible solution to analyze and measure usability metrics during the implementation phase. Specifically, we have developed a framework featuring code annotations that provides a systematic evaluation of the usability throughout the source code. These annotations are interpreted by an annotation processor to obtain valuable information and automatically calculate usability metrics at compile time. In addition, an evaluation with 32 participants has been carried out to demonstrate the effectiveness and efficiency of our approach in comparison to the manual process of analyzing and measuring internal usability metrics. Perceived satisfaction was also evaluated, demonstrating that our approach can be considered as a valuable tool for dealing with usability metrics during the implementation phase.