Abstract: Technology related to detecting and/or mitigating malicious client-side scripts is disclosed. In one example, a method includes sending a request for a page of a client application. In response to the request for the page, the page and a supervisory script of the page are received. The supervisory script of the page of the client application can be executed within a client environment. The supervisory script can override an operation associated with an architected application programming interface (API) of the client environment. During rendering of the page, a call to the architected API of the client environment can be serviced by performing a modified operation that is different than the architected operation associated with the architected API.