Objective The COVID-19 infodemic has been a global public health challenge, especially affecting vulnerable populations such as Syrian refugees with limited internet access and functional, health, digital, and media literacies. To address this problem, we developed Wikaytek, a software to diffuse reliable COVID-19 information using WhatsApp, the preferred communication channel among Syrian refugees. In this paper, we describe the systematic development of the tool. Methods We undertook a pilot study guided by the Humanitarian Engineering Initiative (HEI)'s user-centered design framework, comprising five stages: (a) user research, including needs assessment and desk review of interventions with target users; (b) concept design based on platform and source selection, message format, concept testing, and architecture design; (c) prototyping and implementation, encompassing software development and system operation; (d) user testing (alpha and beta); and (e) evaluation through software analytics and user interviews. We reported a qualitative process evaluation. Results Wikaytek scrapes validated and reliable COVID-19-related information from reputable sources on Twitter, automatically translates it into Arabic, attaches relevant media (images/video), and generates an audio format using Google text-to-speech. Then, messages are broadcast to WhatsApp. Our evaluation shows that users appreciate receiving “push” information from reliable sources they can trust and prefer the audio format over text. Conclusions Wikaytek is a useful and well-received software for diffusing credible information on COVID-19 among Syrian refugees with limited literacy, as it complements the texts with audio messages. The tool can be adapted to diffuse messages about other public health issues among vulnerable communities, extending its scope and reach in humanitarian settings.