Debriefing is essential for effective learning during simulation-based medical education. To assess the quality of debriefings, reliable and validated tools are necessary. One widely used validated tool is the Objective Structured Assessment of Debriefing (OSAD), which was originally developed in English. The aim of this study was to translate the OSAD into German, and to evaluate the reliability and validity of this German version (G-OSAD) according the 'Standards of Educational and Psychological Measurement'. In Phase 1, the validity evidence based on content was established by a multistage cross-cultural adaptation translation of the original English OSAD. Additionally, we collected expert input on the adequacy of the content of the G-OSAD to measure debriefing quality. In Phase 2, three trained raters assessed 57 video recorded debriefings to gather validity evidence based on internal structure. Interrater reliability, test-retest reliability, internal consistency, and composite reliability were examined. Finally, we assessed the internal structure by applying confirmatory factorial analysis. The expert input supported the adequacy of the content of the G-OSAD to measure debriefing quality. Interrater reliability (intraclass correlation coefficient) was excellent for the average ratings (three raters: ICC = 0.848; two raters: ICC = 0.790), and good for the single rater (ICC = 0.650). Test-retest reliability was excellent (ICC = 0.976), internal consistency was acceptable (Cronbach's α = 0.865), and composite reliability was excellent (ω = 0.93). Factor analyses supported the unidimensionality of the G-OSAD, which indicates that these G-OSAD ratings measure debriefing quality as intended. The G-OSAD shows good psychometric qualities to assess debriefing quality, which are comparable to the original OSAD. Thus, this G-OSAD is a tool that has the potential to optimise the quality of debriefings in German-speaking countries.