<![CDATA[Teachers are required to facilitate students' mathematical literacy, but teachers' literacy skills are rarely considered due to the lack of instruments for assessing teachers' mathematical literacy. This study aims to develop a mathematical literacy instrument for teachers, focusing on the processes of instrument construction and validation. This Design-Based Research (DBR) adopts the Tessmer formative evaluation development model, consisting of preliminary, self-evaluation, expert reviews, one-to-one, small-group, and field tests. This study involved two experts as instrument validators (logical validity) and a total of 60 junior high school teachers in Yogyakarta Province to assess readability at the one-to-one stage and in small groups as subjects of field tests (empirical validation). The logical validation results were analyzed using the Aiken V index; readability test results were analyzed descriptively; and the results of empirical validation were analyzed using SPSS. The instrument construction process follows the principles of educational assessment development within the PISA framework and produces 25 literacy items, each involving 10 stimuli with varying contexts. The average V Aikens of 0.95 indicates a valid instrument, while the average readability test score of 4.14 indicates the instrument is in the good readability category. Based on the field test results, each item is valid because it has a Sig value ≤ 0.05. Overall, the question instrument is reliable, with a Cronbach's alpha (α) of 0.860 > 0.7. The instrument can measure mathematical literacy skills among teachers and assess all levels of thinking and question difficulty.]]>
