The ability to compose English L2 emails for Japanese EFL learners at Japanese universities is an important skill, allowing them to communicate with non-Japanese faculty. However, while emailing remains a common mode of communication among faculty and students at the university in which the current study is being carried out, composing an English L2 email text can be a challenge for many learners. In particular, there is little support for the pragmatic aspect of email writing- the interplay between social context and language choices. Further, there is also relatively little pragmatics-related instruction in the EFL classroom, especially in contexts where there are large class sizes, making individualized instruction and feedback from the teacher difficult. Computerized diagnostic language assessment (C-DLA) is one way to address these issues. C-DLA entails a three-stage process- online administration of email tasks; automated, individualized feedback, and the provision of further instruction based on learner performance in the C-DLA. In this ongoing project, we outline the development of a pragmatics-focused C-DLA of English L2 email writing for Japanese EFL learners at a Japanese university. The C-DLA administers email tasks to learners, automatically identifying specific instances of pragmatic failure and providing individualized feedback. The learner is then able to revise their email text based on the feedback from the C-DLA system. We describe the steps of C-DLA development– email task creation, and the administration of the tasks to 426 participants. This elicited approximately 1,300 email texts. The text corpus was manually-annotated for instances of perceived pragmatic failure. Results then informed the creation of a C-DLA prototype. We provide a demonstration of the prototype, and a discussion of the challenges and issues that arose during its development.