In this paper the APA, an App for Posture Analysis, that incorporates the OWAS method (Ovako Working Posture Analysis System) for assessing potential harmful postures of physically hard working employees, is presented and evaluated. The app is intended as a tool for occupational safety experts in assessing the individual postures of workers to identify and prevent harmful working situations in regards to musculoskeletal hazards. For this, APA incorporates a digitized assessment sheet for the OWAS method and timing support that helps occupational safety experts structure and simplify the assessment workflow. To investigate whether the protocol sheet can be replaced with the app, a study was conducted in which the inter-rater reliability among the app and the paper protocol sheet (as control group) was evaluated. In addition, the usability of the app was determined via the User Experience Questionnaire (UEQ). In the study, the app achieved higher inter-rater reliability for watching a video recording of postures than the control group. The chi-square test revealed differences in the use of the app and paper only for leg postures. The UEQ indicated overall above average results, which indicates a sufficient usability, which was also confirmed by free-textual comments of the 13 study participants. The results suggest that it would be possible to replace the paper protocol sheet in the future with an app.