Defining formal and structured eligibility criteria for digital recruitment assistant systems can be a challenging interdisciplinary task requiring collaboration between technical and clinical experts. We introduce crique, a free and open source software capable of extracting formal eligibility criteria definitions from study protocols. The extracted eligibility criteria can be exported to OHDSI Atlas and used in conjunction with the standardized OMOP common data model. In this paper, we present our modular process for the extraction of eligibility criteria, describe our implementation in detail, and show examples of extracted eligibility criteria. We conclude with challenges and propose a strategy to evaluate the accuracy of extracted criteria using our software.