The digital transformation of education has revolutionized second language (L2) writing, reshaping how students compose texts and how teachers assess writing and develop assessment literacy. However, existing research has provided an incomplete picture of what university L2 writing teachers in the Philippines thought, did, and felt when assessments were conducted in fully online learning spaces. Addressing this gap, this study explored how L2 writing teachers understood, enacted, and managed online assessment within the conceptual, praxeological, and socio-emotional dimensions of teachers’ assessment literacy. Using a case study design, semi-structured interviews were conducted with nine university L2 writing teachers, and the multilevel coding method was employed to enable close analysis of their assessment reasoning, enacted strategies, and experienced pressures. The findings showed that within the conceptual dimension, teachers largely viewed online assessment as a continuation of traditional goals while adapting to digital environments. Within the praxeological dimension, they reported redesigning tasks for digital submission and interaction, shifting feedback to multimodal and more iterative formats, and adjusting scoring procedures to fit platform constraints. Within the socio-emotional dimension, they emphasized encouragement, fairness, and trust to reduce anxiety and sustain engagement in virtual classrooms. The findings highlight the need for professional development and institutional support that strengthen teachers’ online assessment literacy across its conceptual, praxeological, and socio-emotional dimensions.