Testing RESTful APIs thoroughly is critical due to their key role in software integration. Existing tools for the automated generation of test cases in this domain have shown great promise, but their applicability is limited as they mostly rely on random inputs, i.e., fuzzing. In this paper, we present RESTest, an open source black box testing framework for RESTful web APIs. Based on the API specification, RESTest supports the generation of test cases using different testing techniques such as fuzzing and constraint-based testing, among others. RESTest is developed as a framework and can be easily extended with new test case generators and test writers for different programming languages. We evaluate the tool in two scenarios: offline and online testing. In the former, we show how RESTest can efficiently generate realistic test cases (test inputs and test oracles) that uncover bugs in real-world APIs. In the latter, we show RESTest’s capabilities as a continuous testing and monitoring framework. Demo video: https://youtu.be/1f_tjdkaCKo. Junta de Andalucía APOLO (US-1264651) Junta de Andalucía EKIPMENT-PLUS (P18-FR-2895) Ministerio de Ciencia, Innovación y Universidades RTI2018-101204-B-C21 (HORATIO) Ministerio de Educación, Cultura y Deporte FPU17/04077