The sp-rest-explorer is a wonderful website to explore all the APIs available on SharePoint. You can find it at https://s-kainet.github.io/sp-rest-explorer For example, if you browse to web > Alert, you can see that the Alert has a method called Add with signature as _api/web/Alerts/Add(…)/. It takes as a parameter, alertCreationInformation which is of type SP.AlertCreationInformation. Read