Web Application Programming Interfaces (APIs) decouple the internal implementation of a service from its consumers which can reuse and compose them to rapidly build new applications.
Many Web APIs are described with the OpenAPI Specification (OAS). The goal of our research is to check the feasibility of using API descriptions found in public open source repositories to study how APIs evolve over time. To do so, we collected a large dataset of OAS documents by crawling open source repositories, we parsed the corresponding metadata and measured the API size in order to extract a simple model to track the lifecycle of API artifacts and observe common evolution behaviors. Our preliminary results indicate that only a subset of the APIs changes, but as opposed to the expectation that APIs should only grow to maintain backward compatibility we also detected a number of APIs with a more variable history. We also study the stability of API artifacts over time and whether APIs are more or less likely to change as they age.