Techniques are disclosed for extending an API using remote, synchronous, user-defined extensions in a microservices environment. A request can be received to perform at least one action on at least one object type, the at least one action defined by an application programming interface (API). At least one extension associated with the at least one action and at least one object type can be determined. An object of the at least one object type and the at least one action can be performed on the object to generate an intermediate object. The intermediate object can be sent to the at least one extension for processing, the at least one extension hosted by a remote service. A response from the at least one extension can be received and the intermediate object can be updated based on the response.