We developed an open-source, rule-based algorithm to automate cause of death coding for analyzing mortality in understudied populations, such as people experiencing homelessness, and dynamic public health crises including overdoses and climate-related deaths.Death categories of immediate public health concern were selected and keyword lists representing each category were developed in consultation with a domain expert. A rule-based keyword matching algorithm was built to assign death records into the selected death categories. The algorithm was trained on death certificate data from five counties across the United States. A case study applying the algorithm to deaths among people experiencing homelessness in Clark County, NV from 2015 to 2018 (N = 646) tested the accuracy of the program against a manual coder.There was strong agreement between the algorithm and the manual coder in the all-cause identification (κ 0.905) and mutually exclusive sorting (κ 0.853) methods. Our findings illustrate the algorithm's ability to accurately classify death certificates into useful categories.This open-source, customizable algorithm may be utilized by researchers, journalists, and others to conduct mortality analyses with publicly available death certificate data, bridging gaps in existing mortality tracking efforts.