Conflicts can be detected between server-side data and client-side data using interchangeable plugins. In one example, a system can receive an interchangeable plugin from among a group of interchangeable plugins for performing conflict detection between server-side data handled by a server and client-side data handled by a client device. Each interchangeable plugin can implement a particular conflict-detection strategy that is different than the other interchangeable plugins and can be selectively integratable into an application programming interface (API) through which the client device is to communicate with the server. The system can integrate the interchangeable plugin into the API to enable the API to implement the particular conflict-detection strategy defined by the interchangeable plugin. The system can then detect a conflict between the server-side data and the client-side data in accordance with the particular conflict-detection strategy defined by the interchangeable plugin.